It doesnt have to be US citizen only. It just has to be who they are claiming to be. If someone in india or europe wants to comment on foreign politics, thats fine. They just shouldnt be able to pretend they are from the US or anywhere else
A town square in Cologne where 90% of participants don't hail from Cologne but London, Mumbai and San Francisco aren't going to solve the problems of Cologne or have any stake in doing so.
Which also reveals of course what Twitter actually is, an entropy machine designed to generate profit that in fact benefits from disorder, not a means of real world problem solving, the ostensible point of meaningful communication.
Upholding at least some utterly basic foundational values of humanity doesn't require holding any stake.
Except human across the planet doesn't even agree on those "foundational values". What seems obvious and fundamental to us, often isn't to others.
Verified residency is better than nothing for putting real money on the table. Although if you've been to a local town meeting, you'll know it's still not perfect.