Everything I dislike about modern social media was a solved issue on a well-run forum: less spam and self-promotion, a tighter community, more toleration for off-topic discussion. When I look at Mastodon, it still has the same blaring "listen to me!" format that Twitter, Facebook, Reddit, etc. all have.
On the traditional forum, the idea of making a thread purely to "share your thoughts" on the topic-du-jour was anathema. Threads were topic-based, not individual based, and the designated personal spaces (post signatures) also allowed for much more creativity – while still not being the primary focus.
Or maybe I'm just being nostalgic.