The "come and go" and "nothing lasts forever" aspects really really put me off. I have an archival personality. I frequently remember a conversation I had five years ago and look it up to re-read it. (This is also one of the many reasons I dislike Mastodon.) I chance across conversations from ten years ago and reply to them.
My first "social media" was h2g2, and everything since has been a downgrade.