Too many people have peed in the pool
I'm not active on twitter, but from what I've seen, particularly in the aftermath of GamerGate, is that it's a putrid mess of hatred, threats, and bigotry. The problem doesn't so much seem to be that people are defending others, but that they are attacking them.I never really saw the point, but it in the past few years it has seemed even more pointless. You just can't have a good, nuanced conversation in 140 characters. You can only shout one-liners and threats. It's what the medium seems designed for.