Bullying is a social phenomenon that creates hierarchies and enforces conformity. It is a reactionary impulse that exists in basically everyone, and even people who don't initiate bullying will often end up joining in as a defense mechanism to ensure that they themselves are not bullied. It is most obvious in children because they do not have fully developed social awareness and will do it extremely blatantly, but of course adults do it as well in more complex ways.

While it is a set of behaviors that I don't think will ever fully go away, I also think that reactionary society feeds into bullying impulses by teaching kids who the "acceptable targets" are and rewarding them for doing it. Getting praise and being ignored are essentially the same reward to a bully, since part of the escalation is seeing how far you can go before an adult intervenes. This intersects with another otherwise normal childlike behavior of testing boundaries, and just like when your kid says a minor curse word and then looks to see how you'll react you have to immediately shut down the behavior in question or they'll assume that what they're doing is fine.

To make it go away you need progressive social structures, unfortunately in late capitalism all social structures outside of the marketplace are either crumbling or gone. If you, your kid, their peers and their parents all met regularly in certain social contexts, the opportunities for bully hierarchies to form would be greatly reduced and those that did could be shut down by adults much more readily - but as it is everyone goes home to their separate houses and apartments and very rarely sees anyone outside of their clique and so it's easy to bully people outside of that clique because there are no social consequences for doing so.