Maybe because a good wrestling match could solve disagreements without the need for further violence? Now, it's like everything is escalated, like they decide to kill the bully instead of giving him a fat lip. Whatever's changed its not the guns, they don't fire themselves.
It would depend on the extent of the bullying, and the physical disparities between the bully and their victim.
Despite what the movies suggest (about Daniel taking karate lessons and finally putting Johnny Lawrence in his place), in the real world, it doesn't always work out that way.
If you have a 130 pound kid taking regular beatings from the 200lbs captain of the football or wrestling team...that bully's not getting a fat lip anytime soon.
Maybe that's part of it... maybe the physical disparities between bullies and their targets have grown larger to the point where some of the bullied kids feel they can't defend themselves the "old fashioned way" like they used to?
Not saying that's necessarily the case, but just an idea.
Even in just the time since I graduated from HS (which was in 2001)...I see some of the wrestlers and football players in high schools these days, and they look like they'd give most adults a run for their money.
I never played football, but I wrestled in high school, and I don't recall anyone on the team ever looking like this:
For a point of comparison, here's what a championship wrestling team for HS looked like in the 80's...
If any of the 3 guys above decided they wanted to be a "bully", and pick on some kid who was 130 pounds, incessantly throughout the school year, that kid's not going to be able to do anything about it, and if faculty opts to not do anything about it, that kid's going to get more deranged and unstable the longer it goes on.