Part of the reason is that people can't just say their opinions online bc they want to be "content creators" instead of real people. So they worry that any hot takes will follow them and affect their reputation. In that sense, being a cheerleader is always the safe choice. Saying something negative invites rebuttals, and people get anxious about posting something that could attract people who love to reply with frothing rebuttals.
But I also hear lots of criticism of OP in my feeds. There's a bunch of professional haters even, who blow things out of proportion just to hate even more. And there is a ton of feminist criticism of OP, especially on Tumblr, but WG users probably don't care about that anyway or are the ones sending frothing rebuttals.
But it's the same with sports or music or celebrities. You can't go marching into the fan space and say things suck without attracting the ones who will call you a doomer, fair-weather fan, poser, whatever.
It's not against the rules to criticize something you've consumed. It's good to think about different perspectives and ways of interpreting art, and those who resist doing so likely have some part of their identity that depends on THE THING (media, band, actress, console wars, whatever) in their life being true and perfect.