Why do we only chant the Hare Krishna Mantra as the main name of God and no other names?

Devotees chant Hare Krishna and no other name as the highest glorification of God.

Why is that?

It is because we are following in the footprints of Lord Caitanya Mahaprabhu who ONLY chanted the the Hare Krishna Maha mantra, even though He said there are millions of names of God one can also chant.

Srila Prabhupada explains why we only prominently chant Hare Krishna as follows -

Srila Prabhupada - "Lord Caitanya Mahāprabhu says that God has millions and billions of names, so any name is as good as "Kṛṣṇa," it doesn't matter".

Devotee - "So Srila Prabhupada, then why do we concentrate on just chanting the Hare Kṛṣṇa Maha Mantra?"

Srila Prabhupada - "Because we are following in the footprints of Lord Caitanya and who only chanted these holy names -

Hare Krishna Hare Krishna
Krishna Krishna Hare Hare
Hare Rama Hare Rama
Rama Rama Hare Hare

So this is why we are chanting this "Hare Krishna Maha Mantra".

Therefore we request you most humbly, there is no loss on your part, but the gain is immense.

If you take to this chanting of Hare Kṛṣṇa, then gradually your misconception of this life will be cleared off.

You will understand your real identity and you will act in that way knowing you are not the material body.

Simply chant Hare Kṛṣṇa.