I think in general a taboo is something the majority of people cannot see themselves doing. If our civilization evolved in a way where you were rewarded for having as many children possible with as many partners as possible perhaps sexual violence would be a feature of video games.

One way to look at it is violence in video games is a mechanism for “completing a mission” (neutralize those preventing it), financial ends, or survival (whether your pursuers have good reason or not). Those things are tangentially related to our day to day lives but the farthest end of what most people might consider themselves capable of doing in pursuit of extreme success or survival. Plus, death is a normal part of life, so is death by force. It’s normalized in modern life.

But in terms of sexual violence, there’s no real world corollary of survival or prosperity mapped to something so heinous. The real life perpetrator feels some twisted satisfaction over another person, but that’s it. It doesn’t preserve an individuals life or advance their station in life. So it’s not relatable to the majority of folks, even in the deep parts of their mind on what they’d be realistically capable of doing to just live or survive.