Mostly because the "damn this is interesting" to "i don't care what you ate yesterday" ratio is not good enough to spend my time on it. These days I am much more enjoying exploring gopher holes, reading and writing blog posts. For realtime communications, I prefer IRC. For me, social media sits in between chatting and publishing content and is therefore neither fish nor fowl.
How on earth do you get people to talk in IRC? Am I missing something? Almost every channel I have joined is dead silent, and any time I tried starting a conversation I felt like I was asking Lebowski for my money.
I do NOT consider the Fediverse and the myriads of implementations of it to be social media, but rather a social web. More like websites with the abilities to communicate and interact in different and interesting ways.
Social media is dead, and has been for a while. Many use it still, but it is not primarily social. The social part was mainly a ploy to get peoples attention and then badly abusing it in ever more creative and sinister ways.
EDIT: This comment was meant to be posted to the parent comment!