I mean... tbf the USA is a lot more homogenized than Europe. e.g. Spain vs. Catalonia, and both vs. France, and all of those vs. the UK, and so on.
But even if that were not the case, you can see how it would be perceived that way - Television portrays this homogeneity as being fairly uniform, regardless of the fact that it is not.
That is always something that I appreciated with sci-fi, like Star Trek Deep Space Nine revealed that despite how Starfleet members were very similar, there were quite a few willing to break out of the mold and behave VERY differently - like becoming terrorists / criminals or whatever. Or like Battlestar Galactica where lets just say that people on some ships behaved VERY differently than people on other ships... or like Star Wars where culture ranged from humans and aliens being slaves on Hutt-controlled poverty-stricken planets (where those in power had everything and the common man could barely survive), all the way over to aliens and humans being slaves on human-controlled planets (where those in power had everything and the common being could barely survive)... oh wait, bad example there maybe:-P.
What bothers me, and this seems more Eternal September than anything else, is how people treat what is happening in the USA as a uniquely USA-only problem... as if the literal exact same thing is not also happening in MANY other places around the globe, plus also slightly different things are happening yet geared towards the same end-point. After all, literally every mystery I have ever read or watched says to follow the money trail... who benefits from what is going on? Exactly.
It's actually somewhat funny in a way: whereas on Reddit it was legitimately true, here on Lemmy the ~~American Exceptionalism~~ USA-centeredness effect seems mainly some Europeans being mad at other Europeans, as some want to share e.g. news about the USA (as if somehow that counts as "news" and "relevant" to "what's happening around the globe"), whereas others do not.
Also, I think you know more than most here just how many bad actors there are across the Threadiverse, spinning up bot accounts or even human ones to amplify some things and decry others. So I am ignoring that here and just focusing on what seems a genuine disagreement.
Funny enough, PieFed provides so very many tools that could help with that - post flairs (e.g. posts in a "politics" community could be forced to be labelled as "USA", to allow people to filter those out?), hashtags (likewise), keyword filters, multi-community Topic Feeds (so you can combine "usa politics" with "world politics" into a single combined "meta community") plus combining comments across crost-postings, all of which help combat the fragmentation effect that Lemmy has no solutions for (currently). But as with all of the above concerns, and again remember Eternal September, it is far easier to complain than to work to actually solve any problem.