It's maybe worth remembering there was a time, when #twitter was really exceptional. Remember when #tweetdeck and hootsuite first came on the scene and the #apis still allowed userstreams? That was the zenith.
I think what really broke it was #celebrity #culture, or more specifically the culture of protection that grew up around them, where they could get away with saying anything but the likes of you and I would be restricted at the first complaimt.
Instead of a #conversation it became another broadcast media for those with the loudest speakers.
That's when the slow death of twitter set in