Perhaps it is just an oversight? Science fiction writers aren't perfect.
I asked a friend of mine who's a Sci-fi enthusiast. He said ' I think SF creators have the unspoken idea that there will be no such thing "in the future"...'
The author of the linked article addresses that: "Contrary to ableist opinion, a utopia is not a world where disability is a problem that’s been solved; rather, it’s an inevitable expression of genetic variance, and disabled humans are not just welcomed but fully included."
I showed that to my friend and he didn't really respond to it. I was kind of hoping to get more from him on the subject but he seems reluctant to explore it.
The truth is, most people don't have close contact with people who have disabilities. It's not something we deal with or think about on a daily basis so I suspect that an author who's not close to anyone disabled isn't likely to ponder how a disabled character might fit into a story.
I think if one did ponder it they might find some very interesting avenues to follow, and if this opinion piece sparks some thought along those lines that's a good thing. But my attempt to discuss it with my buddy didn't reveal much curiosity for exploring it.
Hardcode sci-fi fans tend to view opinions by casual consumers of the genre (like me) as an annoyance so I don't push too hard to discuss it with them.
I don't see what justifies a generalization that SF authors generally ignore disabilities. Without doing a large survey, or a statistical analysis, there's an influential story by one of the most famous SF authors that comes instantly to mind, and it was written 3/4 of a century ago:
https://en.wikipedia.org/wiki/Waldo_(short_story)
Heinlein also wrote multiple stories with blind main characters.
Granted, I haven't read much SF in the last 20 years, so maybe they stopped writing about disabilities.
How ridiculous. As someone with a disability and having spent much time around others with various physical disabilities, I would jolly well hope that the the problem's been solved in the SF future and we'd sure as hell be the first in line to get fixed if treatments were available.
Yes, most of us disabled are 100% "ableist" because having a disability is, unsurprisingly, rather difficult and unpleasant.