>but I simply don’t get why we don’t hold the social media platforms accountable for the content that gets posted to them

I think that's probably too crude a concept, although you can argue that probably 10% of Twitter needs a lawsuit being horrid people and all.

My own guess is that the ability of social media is strong and subtle enough to avoid any rule you might cook up. Their ability to steer enough votes to win an election is obvious and their own bias is clear.

You're not going to get your relatives to leave Facebook, it's too handy for trading baby pictures, so I have no clue what should be done. There'll always be some sort of editorial control.