To a certain reading, this is user-centric: it’s increasing the size of the audience pool beyond that of shared language speakers and readers to the entire literate human race. This is an important point to acknowledge, because every silver lining has its cloud.
It's not about being mandatory. It's about having a privileged position and using it to extract value from people.
The nature of network effects is such that once a site gets as big as reddit (or facebook or tiktok or whichever), it's nearly impossible for competition to take over in the same design space.
Many communities (both small and large) are only present on specific platforms (sometimes only one) and if you want to participate you have to accept their terms or exclude yourself socially.
If they have a privileged position, it is earned and freely given. No one is obligated to use the site. The issue is more one of the commons being enclosed and encircled by corporate interests, and then branded and commodified. Once the deed is done, there is no reason for folks to leave, because everyone they know is there.
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.
