That's coz kids aren't being bullied enough.
the bullying thing is a bit of a wrong conclusion, a large problem with our society is that it's a society that doesn't facilitate bullying, but it's not the bullying itself that made it healthy, it's the oragnic nature in which bullying was possible
we have bullying now, tons of it in fact, i'd argue probably even more than ever, but it's very curated and has an unearned false sense of justice to it that organic bullying never did, kids can learn to deal with bullying that is organic and social in nature. bullying was never something 'enforced'.
much like how living in an organic environment where disease exists is good for one's immune system, it's not the random introduction of disease that's healthy, it's the fact that the environment can support it, and thus can also support beneficial growth alongside it
coming up a person who has been isolated from proper socialization and had their whole social existence sterilized and just randomly bully them, is no different than randomly introducing the common cold to a kid who lived their whole life in a sterile pod
you have to grow alongside it, it's not just one factor that can be tossed into the soup