Potentially culture. There's a lot of supernatural events that are reported everywhere (not saying they're real). It's entirely possible that American culture m

Potentially culture. There's a lot of supernatural events that are reported everywhere (not saying they're real). It's entirely possible that American culture means those kinds of events are more likely to be interpreted as UFO sightings as opposed to another kind of event. A lot of sightings are also aircraft tests (IE: B2 bomber), so it could be that other nations test less alien looking aircraft. The New Generation Fighter in the EU looks like an F18, so a mistaken identity is probably going to skew to "fighter jet" and not "ufo".