> I don't know, but I imagine it has to do with the fact that people making social networks are either companies wanting to make money or P2P activists who want to make a thing completely without servers.
Except it has been done. In fact, that’s literally what KaZaA was with its “superpeers”. And what they realized was that by making a semi-decentralized system, they just introduced the weaknesses of both systems (slow downloads via peer-latency and network limits + easy censorship by killing relays/nodes). In addition, this is exactly how IRC works, despite the fact that it’s mostly used with a few nodes these days.
I’m not against semi-decentralized systems. They’re great and help deal with some scalability problems; but they don’t solve for the number one issue most people moving to decentralized are seeking (anonymity, privacy and free speech), so it’s not fair to compare it to platforms/protocols that do offer those features.
