And what would you do? You can't just keep applying residency permits forever, and desperately hoping that you'll get another 3 years. If you don't get approved for another 3 years (during that nerve-racking waiting period), you're screwed. Becoming a citizen is the best guarantee of stability after his actions, and it's not like the US or their allies are going to welcome him with open arms anytime soon.
He also is married and has two children. You aren't going to raise children on a residency permit.