I have wondered a lot about this question myself, and I think the main appeals to me about sexual submission include:

- I am a very self controlled, hard working, breadwinner with a lot of responsibility so not having to be in control or being able to feel like I can "lose control" with pleasure, while being held safely, disinhibits me and is a "break" from normal life

- not having to make all the decisions sexually means I am less likely to be in my head and anxious trying to mindread my partner, I just have to BE and do what he asks and everything will turn out OK

- I can feel looked after and taken care of (again tied to my feeling of being the one that takes care of others in all other aspects of life)

- with my soulmate, fantasies like extreme penetration or being gangbanged by clones of him, are ways to express how deeply I want him to become a part of me, and is tied to my romantic love as well

- being supremely vulnerable in a way that still makes me feel safe is one of the best feelings to me

Finding ways to express submissiveness in ways that do not trigger feelings of unworthiness, punishment etc (unfortunately too much of porn seems geared to those themes, submissiveness tied with inferiority concepts or punishment for wrongdoing), has been very fun for me and my partner. :)