Twitter's business model relies on it being toxic. Controversy and drama generate "engagement", so they have no reason to change. This isn't specific to Twitter even, any ad-supported social platform has this problem and which is why advertising should be considered a cancer.
Couldn't twitter just have a flag for personnel attacks. Or is it considered good that these attacks happen there - plenty I'm sure are potentially supported by a bit more than the one linked from HN. But either way hard to engage with from the outside.