Most communities on Reddit that I’d care to be a part of have additional places to gather, but I do take your point that there are few good alternatives to r/jailbreak, for example.
The host always sets its own rules. How else could anything actually get done? The coordination problem is hard enough as it is. It’s a wonder that social media exists at all.
Gatekeepers will always exist adjacent to the point of entry, otherwise every site turns extremist and becomes overrun with scammers and spammers.