(Opinions my own, obviously.)

I don't think that's necessarily true.

I think large providers would like to say that, but at the scales of cash involved, I think the burden of saying "no we can't be held accountable for what we do, get lost" should be much higher.

If a significant fraction of people are relying on their personal networks to find jobs, even if they're not working in a job where presenting a public face is a key component, then being cut out of large-scale social networking is no longer divorced from your professional life, it's a necessary service.