Fantasy and sci-fi are designed as alternate realities to this world and usually disabilities are expressed through metaphor rather than literal real world disability. A person can’t use magic so they become the worlds greatest artificer and the like.
I’m all for representation, but what is fantasy without being able to fantasize about not having a disability?
Conversely, why would a person want to fantasize about having a disability? I’m not saying there aren’t valid reasons, but I would imagine most people would be doing it in a performative manner.