This is more like a competition than anything, GameJams is an integral part of the indie games communities and something a fair share of developers likes doing.

It’s a way to try to come up with new concepts and get feedback on it. Often with one or more constraints/themes from the specific jam you’re participating in

Veritasium themselves has a video on the topic, they’ve indeed sold parts to investors

Citizens of USA are Americans, but likewise are citizens of Mexico, Honduras and Paraguay