Hmm. This is an interesting question; the answer, for me, is multifaceted.
My husband and I have RPed in an online/in-game setting with various conventions of one type of another since we were newly married almost 30 years ago. So in some ways, it is about escape.
As for role-playing medical or D/s scenes, it is different. On some level, of course, there is an element of escapism. In my professional role, I am a director and have a lot of responsibilities, and a lot of decisions fall to me. I was the eldest child in my family and married a youngest child, so it is not a stretch that I tend to naturally settle into the more dominant role.
So if I get to experience a play exam (an honest-to-goodness one, as it is NOT my husband’s kink at all so he does not particularly slip into the role when I ask), I want the fantasy on an examination table… and that is to not be in complete control. This is not to say I relinquish consent, however.
Another facet, though, is the exploration of the turn-on, and the boundary pushing (again, within the parameters of prior agreed scenario consent). Would I be turned on, in a play exam? Or would I be too shy and chicken out?
Too, is the opportunity to concentrate focus and sensation on a pick-a-body-part/any-body-part for an extended amount of time and even an extended amount of dis/comfort.
Power, sure. Tip-toeing over the line of secret divergence from a norm, something for myself also comes in to play. Curiosity, definitely. Facing fears and slaying them. Exploration and/or escape above all. Multi-faceted.