This is a bit of a silly response on your part. You're not answering the question of WHY people are on FB and not on the little sites like existed 20 years ago before FB. It's called the network effect. You have friends, your friends have friend, those friends have friends. Rather than there being 30 bajillion separate sites representing these friends connections, people go "hey, why not one site with everyone there".
Said little sites may run for a bit and die, and the massive monolith remains, at least until another monolith replaces them.
Well, indulge my silliness for a moment... what if the servers on the internet could talk to each other?
I suspect in just a few more decades, we shall reinvent the 90s and 2000s p2p networks from first principles.
I mean do you remember what p2p turned into for things like downloads? "Some_popular_thing.mov.exe"
They worked great when most actors were well behaved and got abandoned pretty quickly once that changed.
I'm not sure how that applies here? The argument is that a p2p network will be flooded with bots?
There's a p2p network I use today which doesn't have that problem, probably due to its small size. Meanwhile all the big platforms do — including this one!