I think it's about the websites you visit. If you only use "tech-y" or smaller niche websites you don't come across them. But if you visit websites like from the big news media or even niche websites that are not in English. There are filters for all major languages but there are certainly fewer skilled filter writers with time and willingness to write them in other languages.

There's also a gap of websites that are big enough to have this corporativist behavior of putting annoying... objects in their webpages, but not big enough that enough people visit to the point where it's likely that one of them will write the script.

Especially because, like, I do write some stuff for userstyles and userscripts sometimes, but I won't publish them unless I think they'll be useful for at least a small group of people, which I never seem to think will happen for websites in my mother tongue for some reason.