Don’t try to understand it. You aren’t going to get a good answer. It’s a horrible mental illness level of sexual preference.
Anything can be sexualized with enough impulse and experiences. Everyone’s got some weird dark fetish shit. Some of it’s illegal in practice. Normal people bury that shit or only discuss it in therapy. While talking it out so they can hopefully never think about it again.
I’m sure there’s different answers to this just like “why are there serial killers?”. Just be glad it confuses you.