I think it's a lot of reasons.
* Smart phones / Social media have helped make young people more impulsive, more reward-oriented, less able to deal with delayed gratification.
* There's been a turn in the country since Trump ran (partly even since Obama backlash) where a lot of people are more open about their racism and hate. You see far more openly angry people hating on entire groups in public than you used to, a complete erosion of social norms towards decency. Even if the hate existed before, you weren't supposed to show it. Teenagers pick up on that change and have a lot less self-control, so they get into a "well fukk you too then" mood and have less concerns about social norms themselves.
* Covid fukked up social skills development for some kids. In addition, there was a sort of "fukk authority" backlash across the board, you see more people speeding, more people going road rage, more people lashing out in lines or against regular workers. Everyone justifies their own antisocial behavior now because they "don't want to be controlled".
* Police have become even more hostile towards inner-city communities, either expressing open distain to BLM etc. or refusing to police at all, purposely allowing things to get worse.
* Guns are becoming even easier to access than they ever were.