I think that many open source web projects have more and more people from all over the world, I don’t think that it’s all for sure that they are only from North America or Europe, once the project is launched, it will attract people from any place, no matter where the person or group that started it originally ...
However, I think you are right that many open source projects come from the USA, but this is not because they are launched by some boring hobbysit programmer, in fact, many from MIT, the Massachusetts Institute of Technology and other organizations here, including corporations, the Internet, as an industry, has long been based in the United States since it started here again, and it has mature support from organizations here that contribute a lot to projects, some of which end up in open source .. Of course, others month they will catch it over time, I think that it just had more time to take root.