Why do people in BDSM say it’s transgressive?

People in BDSM are always touting about how radical and transgressive their community it is. But honestly I can’t see how it is either of those things. What exactly is radical about a dominant, aggressive, and violent man and a submissive, demure, and pliant woman? Yes I am aware women are doms but the overwhelming majority are men. That’s well known in the community. Plus, women doms often put on a highly sensationalized depiction of femininity so I can’t say that’s transgressive either

I’ve heard the argument that it’s radical because the sub, usually the woman choose this. But still in the end it is the traditional heterosexual, patriarchal relationship dynamic so how exactly is that radical? What boundaries it pushing rather than confirming our already traditional views of sex and sexuality?