This. Whereas rapists almost never just stop at one. The murderer who kills for greed, may consider doing it again, partly because they are willing to place a literal dollar value on human life. The more steeped you are in comitting violence, the more likely you are to resort to it.
But rape is a crime of entitlement. Not just entitlement to sex, but feeling entitled to do whatever you want to another person. Murderers with that mindset are highly dangerous, too… but that’s actually not your garden variety murder.
Basically, the motives for murder vary greatly. The motives for rape, down at the core really don’t.