The difference between forum and a subreddit or discord isn't ultimately the features, it's localism. A forum can make it's own rules whereas Reddit ultimately makes the rules for a subreddit.
The whole point of forums was that it's difficult to make a generalization about them and moreover, what "most" forums did/do doesn't matter. What a particular forum might do in a particular context is what mattered.
When the mods and users dutifully complied with new rules, the admins got frustrated and began curating r/all and r/popular to prevent posts from those subs from appearing.
When that didn’t work, Reddit would then quarantine or ban subreddits based on obvious and organized spam of against-TOS material and subsequent mass reporting of that material by the same individuals.
Once those purges were done they started the enshittification that continues in high-gear to this day.