In the case of plex, it’s not 100% selfhosted. There’s a dependence on plexs public infrastructure for user management/authentication. They also help bypass NAT by proxying connections through their servers so you don’t have to setup port forwarding and can even easily escape double NAT situations.

I can understand paying for that convenience, but cost keeps rising while previously free features continue to get locked behind paywalls.

Tbh, having users required to authenticate with plex.tv was enough for me to look elsewhere. The biggest reason to self host for me is to remove dependency on public services.