They didn’t attack Sweden because they couldn’t gain from an Swedish economic collapse, they did however gain from the falling price of the dollar some time after the attacks. Sweden has not been involved in any shady affairs (at least not publicly known) in the Middle-East, and Swedes are not known as “the great devil” in the middle-east, and Americans are.
Can I instead ask you, why NOT the US?? They are seen as the oppressors, it would be the ultimate honor and a great victory if they hurt the heart of America. It’s not like they pick countries at random.