Prabhupada explains in his commentary to one song that previously when the Lord appeared as Krsna, He established a condition, "First you surrender to Me." But as Caitanya Mahaprabhu, He took that condition away. Instead of surrender, He said, simply just take that which I have come to offer. He didn't display Himself as the Supreme Lord but always as a devotee of the Lord.
Why Lord Caitanya Tries to Remain Hidden - Gaura Purnima, February 28, 2010, Budapest