I believe there are many levels of hate involved.

Some hate because it is a trendy thing to do.

Some hate because their side lost an election and their grasp on power has slipped dramatically.
Some hate because their hold on ideals and talking points that give them power has slipped,even as their side has gained in influence.

Some of all of these folks just hate because others are successful and they just can't stand it.

Last of all some hate because they think that by getting paid a few dollars they will become relevant.

In all of the groups that hate the bottom line is they are just unhappy unless they get a chance to screw up someone else's life.
They are some lonely folks not happy with themselves.