If I had to guess it’s because they see the term leftist as another meaningless term like progressive, which I kinda agree with. I think refusing to be labeled a leftist is dumb but I definitely hate when people say “leftism”

It’s an infantile disorder tbf

I wondered the same thing as you but then I’ve been thinking that I can’t really judge what leftcoms say as a whole based off the comments of a few redditors. So who knows.