Presumably you're browsing english-language Lemmy

Most people are going to want to converse in their native/primary language, and by numbers that means a lot of Americans who are, of course, primarily concerned with American issues

There's also the fact that America is a huge player on the international stage, so American issues can have a lot of repercussions in other countries

And if you haven't noticed, America has kind of a lot of shit going on and there is a lot to talk about there.