I'd argue that raising a bunch of venture capital is what stopped them from being able to be a sustainable business.

I paid for Plex for a long time but I no longer use it because I got fed up of fighting it. (I now use Jellyfin + Tailscale instead.) I think the problem with Plex is they aren't happy with what they are: a service for people viewing their own (yes, pirated) media library. They always wanted to be something more. Netflix envy.

But all anyone I know ever wanted Plex to do was handle their media library, perhaps offer a paid tunnelling system but otherwise get out of the way.