If I had to guess (dont have the fetish, but your question made me also curious so I just did some quick research, for science), it looks like a branch of transformation fetish i.e. body modification, furry, forniphilia (human furniture), inanimate transformation, transgender (the fetish not the identity), etc.. or some kind of twist on a BDSM fetish with a specific focus on bondage and submission. As for why it is attractive to these people with this kind of kink, idk. Maybe there is some mental relationship between different section of the brain which relates sexual pleasure with something less common.
I imagine this fetish's subject matter could span the full spectrum from extremely tame topics to a horrible twisted abomination which even the fire cant destroy.