A serial killer is usually more intelligent than a serial rapist.

Killing is, simply put, the more rational, efficient and terrifying outlet for a psychopath to use to feel like the great monster they want to become famous for being (or unknown for being but enjoy being). Rape, unless ended with kills each time, if done regularly to the same type of victim puts a target on the back slower than the serial killer's victims will put one on theirs. On the other hand, the ability to track a killer who is using gloves and basically leaving zero traces of who they are or where they come from is phenomenally harder than a rapist. Rape could work if you used chloroform and gang raped, or just self-raped the victim in a 'dungeon' room of sort and ensured they left the room with no mark of you on it and you didn't ejaculate onto them or they definitely swallowed it if it was in their mouth but overall it's far more prone to leaving traces of some kind and location wise- killing can be done at a variety of locations, ape has to be done somewhere where no one else is around and you have to keep the victim form making noise if people are around for far longer than a serial killer does. So despite kill victims being a more efficient fast warning signal for a serial killer to be caught, rape is a far easier tracked crime back to the criminal. Another factor is the learning and mastering if weapons and combat is far more difficult intellectually than mastering drugging someone and abusing them once they’re already tied up. Some serial killers drug their victims first to make it easier but may need their victims sober for the simple thrill of the chase. There is far more demanding training to be an amazing serial killer than there is to be an amazing serial rapist. Both serial killers and serial rapists obsess over a particular ‘type’ of victim. They have some nightmare(s) from childhood that they need to get the hell over but can’t. Killing that person is a far more understandable way to ‘get back’ at the world and also ensure no one is left alive who knows that filthy part of you exists while raping them is frankly just barbaric and doesn’t ‘get back’ at anyone other than the one you’re raping. Killing is in itself symbolic to begin with as it’s only going to really harm those alive who knew the people the long run. Raping just targets that victim type and irrationally tries to solve the unsolvable (the trauma of the persons’ childhood). Serial killers tend to train form the get go in life. A dead rabbit here, a dead dog there but serial rapists first practice on the actual real human victims… That’s a major problem. They not only have never done it before and may fail to complete the rape but the person may themselves be a serial rapist or killer and take revenge on them. On top of this the fact they don’t kill is horrendously irrational, that victims can run and tell any time they want. Serial killers can target both animals and humans as well as both people they know well and people they barely know. Rapists can only target either people who barely know them or people so mentally weak it’s simply pathetic and not a fair fight to begin with.Take the average serial killer and put them in a ring with a serial rapist. The rapist has a great early game, overpowering the killer, grappling like a bear and pingnign them down in no time utnilt he killer says 'okay mate, time to show you real martial arts', and has snapped their neck with their feet jumping up from the floor in no time.