Not trying to defend the engineering by any means, but the culprit seems to be the product. Since its inception, Twitter has had its roots in freedom of speech: if your government is giving you shit, you post stuff on twitter. If main stream media is giving out propaganda, you tweet about what you think is the real issue. Because they're so liberal about allowing any kind of contents, their anti-abuse algorithm is deliberately overlooking a lot of things. And it's a fine line between some kid giving crap about Trump and some kid sending out death threats. These are really hard AI problems. Unless you go gung-ho with rule-based algorithms (if tweet contains "f&*k": blacklist user) you aren't going to surgically extract the bad posts. And that's a really labor-heavy solution that engineers don't want to do (and look down upon).
Other companies have taken the path of preventing abuse completely. If you start saying hate rants on Facebook, Facebook is super liberal about suspending your account forever. Twitter can't do that because their entire product is meant to be a ventilation outlet for many users. And these are by the way their die hard users, so you don't want to piss them off. So they're at a crossroad of 1) re-shifting their product to broadcasting outlet like ESPN (at the expense of losing the mainstream twitter users), or 2) staying as minor, niche-market product to keep the existing users. I would personally like 2), but of course 1) makes more sense given their state as a public company.
In contrast, if you look at LinkedIn's feed, it's even worse. It still amazes me there can be so many ignorant people even in the tech world. Their comments are meaningless, shared articles are crappy. And their problem is lack of content / ecosystem (i.e. not enough professionals would liberally share stuff on such platform) - I think they should just shut down the feed and keep acting like an online resume repository..