It doesn't really matter why Americans are have a lower rate of bi/multilingualism, really. Having familiarity and exposure to other languages does not automatically grant one the ability to communicate with everyone. Europeans might have proficiency in more languages on average than North Americans, but that doesn't mean that if a bunch of Hindi-speaking players were dropped into EU groups that affected players would get by on the grace of their superior language exposure, nor does it mean that the appropriate solution is "learn Hindi."
I very much support the idea of everyone know multiple languages, regardless of where one lives. I know two languages and have studied two others on a university level, and I very much wish I had the time and skill to expand that. But issues like this ("I can't talk to some of the people I play a video game with") need to be addressed with practical solutions not philosophical debates.