> Social media is valuable, that’s why people use it.
That doesn't follow. Neither of those two statements seems self-evident.
People typically follow social media for a number of reasons and to my mind novelty and the pretense of a sense of community are the biggest one. But the latter is usually just paper thin. In "successful social media" most social interactions are either fleeting or superficial. You argue on the Internet with strangers and you pigeonhole them to fit your biases. The entire focus for social media is to drive up "engagement" because clicks and views mean more ad revenue and a bigger "audience". And as the effort of providing something genuinely interesting is a lot higher than something provocative (which has the benefit of being able to simply be an outright lie), that's where social media inevitably trends towards.
Pre-social media spaces were a lot more social in the sense of being communal: IRC chat rooms would have old guard regulars, often lurking around in case something interesting pops up; moderation would happen very bluntly and immediately to set clear house rules about what is or isn't acceptable behavior. Forums had a much lower frequency but followed similar patterns. There was a clear sense of a shared culture if you stuck around long enough and people would actually avoid hanging around in the extremely large forums or chat rooms because they were "too noisy" to have a conversation. It would usually be where you'd go to seek advice or help you couldn't find elsewhere and any follow-up would usually happen in a more confined space like DMs.
What social media has effectively done is looked at the extremely large and noisy spaces and decided that this is what everything should be like by default and then bolted on some ways to keep track of what conversations you were having while mixing the ideas of "people that seem interesting/nice" and "accounts that post interesting content", productizing and transactionalizing all social interactions. Even Mastodon is guilty of this but on the smaller instances at least the scale is limited by default.
The problem with social media being the "marketplace of ideas" is that you normally go to the market to get new things and then you go to work, go home or go to your "third place" (e.g. your peer group, your pub, your club house) where you can all show each other what you got. Social media wants to be all of those places but because the marketplace is the only part that makes money, that's all it delivers.