Not him and Kaa doesn't do it fir me more than anything else but for me it's 2 things
1. A loss of control on either party's part, and a loss of responsibility for the subject
2. Years of listening to actual hypno files and their effects have probably conditioned me to associate hypnosis with pleasure and sexuality.
Also in general, I'm into sexual situations where one or both memebra really, really want it, and hypnosis can make you really, really want it even if you don't want it.