It's hard if you want it to be a social network, and hard if you want it to be under one domain. If it's a forum to talk about hats for cats at hatsforcats.lol

It's hard if you want it to be a social network, and hard if you want it to be under one domain. If it's a forum to talk about hats for cats at hatsforcats.lol that's not hard, and that's pretty much what the web was pre-Facebook. Is Reddit/Twitter "better" because everything is in one place? Maybe. But then it's a hard problem that requires money, and we end up where Reddit/Twitter are today.