Why?
Because most Americans still can't believe that there are people living outside of America.
Because these are American products produced in (American) English. I suppose it's not crazy because Hollywood seems to be the best in the world at producing movies that please the masses as of now, but it is interesting.
They insert subtitles for countries that aren't English-speaking, so language really isn't that much of a barrier.
American movies are definitely one of the most influential American exports. With their worldwide market base, only the Hollywood studios can afford to make lavish films with state of the art special effects and global superstars with budgets of $200 million.
This was not always the case. At some point there was a watershed. Assuming that the data presented for X-Men films is accurate, X-Men 1 had a larger domestic take than international. And that movie had subtitles as well, so thanks for being patronizing.