Twitter works quite well to captures some thoughts you just have on the moment. Though of course the reader experience is awful. The blog post format somehow implies more work and preparation, where you can just open twitter, start to write a short line, then continue message by message.
I don't know why twitter doesn't even try to improve the reader experience, threads are just a complete mess.
Twitter essays are definitely perceptually worse than blog posts.
It's where the audience is. It's working better for getting messages out & people actually reading them than any alternative, despite sucking.