Why haven't libel laws caught up to the social media age?

I'm hoping a lawyer can weigh in on this. I was reflecting on how social media has demonstrated that people with influence (i.e. a lot of followers) can now effectively destroy individual people's livelihoods. It seems to me that, in at least some of these cases, this could be construed as a crime.

I'm wondering why libel laws haven't fully caught up to this new reality. Is it simply because the legal system is more glacial than the tech industry or is it because it's a very thorny issue with implications for free speech and tricky concerns around establishing liability? Both?

EDIT: This is referring to the US.