Why Something Rather Than Nothing?

[Mister Agenda]

You seem to have a decent case that omniscience is impossible there, I give you that. But God doesn't HAVE to assert that he's God, he can accept it as tentatively true for practical purposes while still recognizing that he can't really know.

Accepting as tentatively true while recognizing it might be otherwise....is essentially an assertion in my opinion.

as·ser·tion/əˈsərSH(ə)n/
noun
a confident and forceful statement of fact or belief.

Your opinion seems to be largely dependent on what will best serve the cause of making you feel like you're winning an argument in the moment that you say it.