The MIT license requires you to attribute the original authors, I would assume.

Public domain rights differ across countries. So someone could put a work into the public domain and sue you in the one or two major countries where copyright can’t be disclaimed by the original author without a license, or where there isn’t legal precedent for it (this is purely theoretical and has never actually occurred before, it would also not be likely to succeed if it did happen).

Also, it is technically possible for someone to claim public domain software as entirely their own work, while MIT requires attribution.