I think he just wanted to fight Deontay to have fought all of the three kings. He had floated a fight a very long time ago when Fury wouldn't fight him, so I think it is a personal goal.
Usyk fight story concluded with the second Dubois win. With that win he no longer owes boxing anything else, especially after vacating his belts so the next era could have at it. He’s here now to cash out, and he’s earned it.
My understanding is that he wants a big fight in America. None of his previous fights here weren't especially big. Deontay Wilder is unfortunately the biggest HW we have.
Also Wilder legacy, even more. No one had beaten Usyk until then, let alone knocked him out... in your scenario
You never know. Put some money on it. I'd imagine the odds would be pretty good - not crazy, but good.
Money. He talked a lot about wanting to fight in a world championship match in Ukraine, but he threw away the belts + Wilder in America.