Śrīla Rūpa Gosvāmī explains why only Krsna always has 64 qualities in full.

It is to be understood that the aggregate number of qualities of Kṛṣṇa is sixty-four. 

Śrīla Rūpa Gosvāmī has attempted to give evidences from various scriptures about all sixty-four qualities present in the person of the Supreme Lord Krsna.

Srila Prabhupada - "Śrīla Rūpa Gosvāmī, after consulting various scriptures, has enumerated the transcendental qualities of the Lord as follows:

(1) beautiful features of the entire body;

(2) marked with all auspicious characteristics;

(3) extremely pleasing;

(4) effulgent;

(5) strong;

(6) ever youthful;

(7) wonderful linguist;

(8) truthful;

(9) talks pleasingly;

(10) fluent;

(11) highly learned;

(12) highly intelligent;

(13) a genius;

(14) artistic;

(15) extremely clever;

(16) expert;

(17) grateful;

(18) firmly determined;

(19) an expert judge of time and circumstances;

(20) sees and speaks on the authority of Vedas, or scriptures;

(21) pure;

(22) self-controlled;

(23) steadfast;

(24) forbearing;

(25) forgiving;

(26) grave;

(27) self-satisfied;

(28) possessing equilibrium;

(29) magnanimous;

(30) religious;

(31) heroic;

(32) compassionate;

(33) respectful;

(34) gentle;

(35) liberal;

(36) shy;

(37) the protector of surrendered souls;

(38) happy;

(39) the well-wisher of devotees;

(40) controlled by love;

(41) all-auspicious;

(42) most powerful;

(43) all-famous;

(44) popular;

(45) partial to devotees;

(46) very attractive to all women;

(47) all-worshipable;

(48) all-opulent;

(49) all-honorable;

(50) the supreme controller.

The Supreme Personality of Godhead has all these fifty transcendental qualities in fullness as deep as the ocean. 

In other words, the extent of His qualities is inconceivable.

As parts and parcels of the Supreme Lord, the individual living entities can also possess all of these qualities in minute quantities, provided they become pure devotees of the Lord. 

In other words, all of the above transcendental qualities can be present in the devotees in minute quantity, whereas the qualities in fullness are always present in the Supreme Personality of Godhead Krsna.

Besides these, there are other transcendental qualities which are described by Lord Śiva to Pārvatī in the Padma Purāṇa, and in the First Canto of Śrīmad Bhāgavatam in connection with a conversation between the deity of the earth and the King of religion, Yamarāja. 

It is said therein, "Persons who are desirous of becoming great personalities must be decorated with the following qualities: 

truthfulness, 

cleanliness, 

mercy, 

perseverance, 

renunciation, 

peacefulness, 

simplicity, 

control of the senses, 

equilibrium of the mind, 

austerity, 

equality, 

forbearance, 

placidity, 

learning, 

knowledge, 

detachment, 

opulence, 

chivalry, 

influence, 

strength, 

memory, 

independence, 

tactfulness, 

luster, 

patience, 

kind-heartedness, 

ingenuity, 

gentility, 

mannerliness, 

determination, 

perfection in all knowledge, 

proper execution, 

possession of all objects of enjoyment, 

gravity, 

steadiness, 

faithfulness, 

fame, 

respectfulness, 

lack of false egotism. 

Persons who are desiring to become great souls cannot be without any of the above qualities, so we can know for certain that these qualities are found in Lord Kṛṣṇa, the supreme soul.

Besides all of the above-mentioned fifty qualities, Lord Kṛṣṇa possesses five more, which are sometimes partially manifested in the persons of Lord Brahmā or Lord Śiva. 

These transcendental qualities are as follows:

(51) changeless;

(52) all-cognizant;

(53) ever fresh;

(54) sac-cid-ānanda (possessing an eternal blissful body - vigraha);

(55) possessing all mystic perfections.

Kṛṣṇa also possesses five other qualities, which are manifest in the body of Nārāyaṇa, and they are listed as follows.

(56) He has inconceivable potency.

(57) Uncountable universes generate from His body.

(58) He is the original source of all incarnations.

(59) He is the giver of salvation to the enemies whom He kills.

(60) He is the attractor of liberated souls. All these transcendental qualities are manifest wonderfully in the personal feature of Lord Kṛṣṇa.

Besides these sixty transcendental qualities, Kṛṣṇa has four more, which are not manifest even in the Nārāyaṇa form of Godhead, what to speak of the demigods or living entities. 

They are as follows.

(61) He is the performer of wonderful varieties of pastimes (especially His childhood pastimes).

(62) He is surrounded by devotees endowed with wonderful love of Godhead.

(63) He can attract all living entities all over the universes by playing on His flute.

(64) He has a wonderful excellence of beauty which cannot be rivaled anywhere in the creation.

Adding to the list these four exceptional qualities of Kṛṣṇa, it is to be understood that the aggregate number of qualities of Kṛṣṇa is sixty-four.

Śrīla Rūpa Gosvāmī has attempted to give evidences from various scriptures about all sixty-four qualities present in the person of the Supreme Lord Kṛṣṇa." (Nectar of Devotion 21)

Srila Prabhupada - "It is described that Kṛṣṇa, the enemy of Kaṁsa, has sixty-four transcendental qualities, and all of the ever-liberated souls who accompany the Lord have the first fifty-five of the qualities, without any doubt. 

Such devotees are related to the Supreme Personality of Godhead in any of five transcendental mellows—namely 

neutrality, 

servitorship, 

friendship, 

parenthood 

conjugal love. 

These relationships with the Lord are eternal, and therefore nitya-siddha devotees do not have to strive to attain the perfectional stage by executing regulative devotional principles. They are eternally qualified to serve Kṛṣṇa." (Nectar of Devotion 25)

Srila Prabhupada - "So a Vaiṣṇava devotee of the Lord is expected to have all good qualities. 

The more you become advanced in Kṛṣṇa consciousness, all the good qualities that were covered by the cloud of māyā will come out. Good qualities are already there. 

Just like Kṛṣṇa has got sixty-four good qualities in full, and we are minute particles of Kṛṣṇa; therefore we have got also those good qualities in minute particles. 

But these good qualities are now covered. Just like fire is covered by the ashes. So it does not act. 

Although there is fire, but when it is covered with ashes, it does not act. So we are fire. Kṛṣṇa is fire; we are also fire, in quality. 

There is a very... There is a big fire, blazing fire, and the sparks. The sparks are also fire. 

Therefore we sometimes desire to imitate Kṛṣṇa. 

Because we have got these qualities in minute quantity, so we think that "I am God, I have become." But we do not know the quantitative difference. That we forget. 

We can say we are God, but teeny God, not the Supreme. 

Spark. Fire, blazing fire, and the spark. Now, this quality, fire, this also becomes almost unseen when we are in this material world.

Just like if the fire sparks fall down out of the blazing fire, it becomes extinguished. 

So in order to ignite again our fiery quality, we must go back to the original fire. Then the fiery quality, the brilliant fiery quality, will again be exhibited." (Lecture on SB 2.3.13-14 - Los Srila  Angeles, May 30, 1972)

Srila Prabhupada - "First of all, what is the conception of God? Conception of God is "God is great." 

Nobody is greater than Him, and nobody is equal to Him. That is God. Asama-ūrdhva. 

The exact Sanskrit word is asama-ūrdhva. Asama means "not equal." Nobody can be equal to God. 

This is analyzed by great ācāryas. They have analyzed the characteristics of God. 

They have characterized the characteristic are sixty-four. And out of that sixty-four, we have, we living entities, we have got fifty only. 

And that is also in very minute quantity. 

Fifty qualities of God we have got, but that is in minute quantity. 

Take, for example, just like God has got also the tendency to love young girl. Take it for a crude example. Just like God is dancing with young girls. 

But we have also the same tendency. We also want to be surrounded by young girls and dance, we enjoy. 

But the thing is that you can enjoy in the company of a few girls. That is minute quantity. 

But God can dance with unlimited number of girls. That you cannot. These are crude examples.

So these sixty-four qualities, they have analyzed that we living entities, we have got in minute quantities. 

And amongst the living entities, the highest perfection is to be seen in the life of Brahmā, who is the chief living entity within this universe. 

So similarly, Lord Śiva has got fifty-five. Lord Nārāyaṇa has got sixty. But Kṛṣṇa has got in full sixty-four. Cent percent, hundred percent all the qualities.

Therefore either Lord Śiva or Lord Brahmā or the living entities, nobody can be equal to Him. This is the conception of God." (Lecture on SB 5.5.1 - Los Angeles, January 20, 1969)^^^.