I think Reddit must be incredibly astroturfed by bots. As soon as you go to literally any other site, they are usually hardcore "right wing" by Reddit's standards. 4chan, Facebook, news site comment sections, random forums (eg. bb.com misc section). I think Reddit must be some attempt at propagandizing the internet to be left-wing.

Also mod teams are likely highly infiltrated so they ban a lot of dissent as well.