A group called Collective Shout lobbied payment processors and banks to stop supporting platforms like Steam and Itch.io due to some NSFW content on them. So Steam and Itch.io responded by removing the offending content.

So pretty much Steam and Itch.io were being forced to censor legal content, hence people are angry. Collective Shout markets themselves as feminists fighting for women, but they have ties to Christian anti-pornography groups, and in reality, probably want to remove as much pornographic and queer media as they can.