Who benefits

Because they have such a low opinion of themselves they try to make themselves feel better by cutting someone else down...
NO ONE benfits..

Some never knew anything else and just repeat behaviour they saw at home and think that's how things work. Some do it out of envy and insecurities. They can't accept the fact that someone else is better at something than them and have a compulsion to "punish" them for it.
Some just have very rigid idea of how things should be a if you somehow disturb their fragile world it shakes them to the point they feel urge to attack.

Misery loves company, maybe. If they make others miserable like them, then they won’t be alone. Even if they don’t think that’s the reason they do it, it likely is.

To promote, massage and elevate their own broken, corrupt and sociopathic egos. 😊🌺

It alleviate their own stress and failures. It’s easier to direct attention.

selfishness at its best

Because they are nothing. That's why.

Smh. Because someone belittled them first.. sad.