The reason for anything large usually has a lot of contributing causes, and I don't think I have all of the answers here, but a first guess would be to think ab

The reason for anything large usually has a lot of contributing causes, and I don't think I have all of the answers here, but a first guess would be to think about US Cultural Dominance. If the real world was a game of Civilization, the US would be having an overwhelming cultural lead after WWII. Basically whatever the zeitgeist in the US is ends up spreading through the world for many reasons. If it dominated American culture 50 years ago that going to college was mandatory, it seems likely that this attitude would have spread to a lot of other countries too. Is that the right explanation? Probably not entirely, but I think that attitudes and ideas that dominate the US end up spreading a lot because of Hollywood and other cultural reasons.