Have any of your friends installed a Facebook app? Because it doesn’t matter if you decide they're not worth using, you have to make sure nobody in your network uses them either.

A lot of people like using them as a login system. Maybe WebAuthn will help with that since it’s a valid use but most people didn’t see what else they were agreeing to.

The other thing I’ve seen a lot of people use are notifications / invites. e.g. most big gaming communities are bad experiences but you can bootstrap your friends into a better group. That seems harder to change and it’s definitely a real need.

Services like Buffer.io or custom mobile/desktop clients that post on your behalf.

Basically only automation & power users.