I think when hitbox caught on is when twitch started muting VoDs to crack down on people streaming music, since they can't really do the youtube thing of just funnelling revenue back to the copyright holder. The system had a bunch of issues, like muting in half hour segments rather than specific instances, and false positives on game soundtracks and stock sounds, plus the predictable bunch of people getting pissy that they couldn't stream all the music they wanted. Hitbox didn't worry about that, and also tended to be a little more stable and more helpful, probably just because they didn't have huge streams pressing their servers and huge idiots pressing their support teams, so a lot of people (mostly smaller streamers, I think?) switched, or at least floated the idea of it. A lot came back when their viewers wouldn't obediently follow, and the system has improved a lot anyway.
I haven't used hitbox in a long time, but I've not had any issues with twitch lately, as someone who uses it near daily. Honestly I haven't heard anyone even mention hitbox in probably a year, did you have some particular reason for considering it beyond just checking out all the alternatives?