I’d say one downside with those buildings is that sound travels really easily between neighboring apartments and they often tend to get quite cold in the winter, although I’m not sure how other buildings from the same time period compare.
Definitely beats being homeless though.
The network effect is one reason, if users are responsible for the content then there will be a shortage of content until enough users join.
Beyond that, humans are social creatures and want to fit in. If your community mainly hangs out on one platform, people will want to be a part of that platform. What helps is if people with a large enough following or entire communities make the decision to change platform, but that can be tricky.
Now I’m thinking about making badges that say “Assigned Child At Birth”.