My inkling is that it has to do with wealth of the society and social protection. In many countries of Europe, people aren't as beholden to companies for livelihood, and can thus better afford to spend personal time on projects they care about. There's a better social conscience. In India, at the opposite end, those same skills put you above social average and are a valuable tool that you wouldn't want to give away for free (unless you're from an affluent background).
This is, of course, just my feeling and not backed by any actual research :)
a) it's in the water b) we are a bunch of socialists c) we are trained from when we are young that money is ugly
Actually, There is a lot of open source coming out of the US as well. But there are a lot more possibilities in the US to get good funding for software projects and there is a strong culture of "making it" in the US, which probably influences things towards more proprietary.
"Just the fact that people are being surveilled inhibits their ability or feeling that they have the opportunity to do new and creative and innovative things. So that kind of reduces their risk taking basically, which in turn means you get less and less creativity and innovation and more and more stagnation of civilization. That's what happened in the Soviet Union. That's what happened in East Germany and the Communist plot. They stagnated because people were being so surveilled that they were afraid to do things. It made people afraid to take a risk."
https://www.youtube.com/watch?v=WgbJqFrwhbw&t=9m38s
When the description of a project is "We are a federation of microbloggers who care about ethics and solidarity and want to quit the centralised capitalist services", I can see why citizens of a police/surveillance state might not be inclined to create or work on it, even if subconsciously. But I could be wrong; Europe seems pretty heavily surveilled too.
That led to an active European freeware, shareware, and eventually open source software scene.
It's an international project. The lead developers are in Europe, admins are in North America, servers and users are all over.