they are popular because they provide simple answers to complex issues.

People like that. Esp younger folks.

Just like the alt right is so popular with them, because it gives them simple answers.

Left doesn’t have simple answers. Wants you to listen to a college course type of lecture on every issue… people don’t care about that. They want a simple soundbyte they can emotionally respond to. Left is very poor at that… there are some examples, but they dont’ really get much traction outside of leftist/socialist circles.