The real problem is that school personnel don’t want to deal with the parents of the actual problem kids, so they get away with it even under zero tolerance.
^ this. Every time the school staff have to deal with THOSE parents, yet again, is a huge stressor and they will try to avoid it if they can, but the parents of the "generally-good-except-this-once" kids will generally be totally reasonable and easy to deal with, even if injustice is occurring.
How hard is it to just expel them? They seem to expel victims with ease...