That's a bit of a chicken-egg problem, as Tor still lacks a killer app. A popular Tor-only forum might just be what it takes to drive wider adoption.
There is also the issue of it being super slow.
Notably, keeping javascript enabled during "Tor mode" even if the user has explicitly disabled javascript.
https://community.brave.com/t/tor-mode-always-has-javascript...
I recommend using Tor browser and using about:config to set javascript.enabled to "false".