Rioting feels good. Hell, destroying stuff indiscriminately, threatening people, and setting fires while people cheer you on, that's gotta be the ultimate catharsis.

All it takes for a mob to devolve into rioting is a single asshole. All of the cities telling their cops to stand down or otherwise avoid the riots, all the district attorneys dropping charges against rioters, they are perpetuating this. One might say they're doing it on purpose.