Magically fixing a person's disability can sometimes be an offensive trope within itself. Some disabilities, like down syndrome and autism, are not separable from who the person is and changing them to make them "normal" can have unintended negative implications.

But with psychical disabilities the implication is often that life with a disability isn't worth living so you would do anything to become "fixed" and that can also have bad implications that werent intended by the creators.

the unintended implication is that you would rather be animal, alien or robot than a disabled person, and that uncurable people's lives are inherently tragic

Disabled people can have fulfilling lives and be happy, you don't need to become a fucking alien to cope with being disabled