... I am a non-anglophone who, at the time of Facebook's raise to social media dominance lived in multiple non-anglophone countries. I was there.
In one of the places I lived there was briefly a popular local Facebook alternative. It lasted maybe a couple of years before entirely capitulating and getting absorbed. That place does still have a local Reddit-like alternative, and Reddit is certainly more US-centric. You are right that Facebook stayed popular much longer outside the US. It has started falling off in some of those places, but I did keep a Facebook account for work purposes for a lot longer than you'd expect because work relations in those territories would share Facebook credentials as a way to establish professional contact. Twitter may as well have been a lost ancient civilization, though.
There's also a lot to unpack in the assumption that on a thread about "why do Americans default to assuming everyone is from the US" you're reflexively lumping the entire anglosphere as part of the US, but honestly, I'll let the recently annexed English-speaking countries deal with that one on their own.
