If you think about Reddit as each of its subreddits being little islands, each island has a timeline of user posts, each post has a tree of comments, and there are moderators who enforce the rules of that island.
To me that starts to sound a lot like each subreddit could be replicated as an instance of something like Mastodon, and you're really only some kind of shared user database away from being able to make something that functions exactly like Reddit, but without any corporate control.
The problem with that is that you need to spend money to either host your own instance or pay someone else to do it for you. Most people are tech-illiterate and do not want to pay to host something which doesnt even reach the threshold to be a "hobby"
