If you're talking about 1991's Outlander, that's hardly new, that's 25 years old...
Personally, I like books where you freeze and go "WTF!?" and hold the book away from you lest it bite you. Be this through rape, eating (of/the) babies, or literally throwing a person under a bus. As long as no cat gets hurt. I don't care if it's unethical or glorifies atrocities, I mean, it's fiction, it's not a gateway for me to commit any of those deeds or approve of them in real life. Pokémon is one huge glorification of dog/animal fights. Naruto? Training 12-year-olds to kill and proudly be killed. Or commit suicide because your client needs you to. Like Hamas. And Kony's child soldiers. That is Naruto, folks. And we love it. Don't get me started on Game of Thrones. Would anyone care much for Danaerys had she not been groped by her brother and sold into sex slavery as her personal trial by fire? Who didn't stop short and hold their breath when Arya encountered the pedofile in the brothel? Who didn't go "Whoaaaaa" when Jaime more or less forced himself on his sister that one time? Rape may become cheap, but it will never leave one cold, unlike murder.
Rape has always been and always will be, a cheap plot device, an easy way to justify a character's development and actions. It's an extreme thing to happen to a person, extreme enough to lead to extreme consequences, but not final or irreversible like death. It's the kind of experience many victims will put right second to death for worst things that can happen, so it's the ultimate extreme an author can go to without killing a character. It's readily available, too: rape sadly happens very easily and easily damages a person. Rape can turn a person's personality around 180°, including their attitude, outlook, and will to live, and trigger mental illness.
Rape, the word, creates discomfort. The mere word makes people cringe and think of the worst that can happen to a person. To the reader, rape is 3rd party shame, taboo, horror, violence, humiliation, sex, and all their consequences, all in one act. I have a rape in my MS and I find it hard and extremely uncomfortable to write that word rather than beating around the bush with "what had happened to him" or "that time at the checkpoint".
Rape is also so horrible beyond the physical, that it creates protective feelings and pity in many readers. There are readers who want to hug the character through his/her story, sweat and shiver for them, baby them. It's why we love Hachi, look at that poor foolish dog waiting in the cold for his dead owner to return... Many want something horrible to happen to a loved character, just so they can hold his/her hand and cheer them on.
Some people enjoy gawk-fests, schadenfreude, and witnessing pain. Be it for sadism or, in my case, a need for big feelings and shudders and nails on chalkboard. I've been reading a lot of torture porn lately like The Flesh Cartel or Broken. I don't know if it's my inner sadist or the softy who wants someone to pity, I like it. How do I feel about rape in real life? Death penalty.
As sick as it may be, rape as content is simply universally "appealing", it's easily available and has something for everyone to have strong reactions to, whatever their nature. Get their rocks off, feel outraged, pity the victim, identify,...