In addition to the list of explanations for why disabled people can exist in a fantasy setting that chumbalumber@lemmy.blahaj.zone provided, I’ll also just say:
Using diegetic explanations for why a problematic aspect exists in a piece of fictional media does not address the substance of the problem. The problem is that disability is often not represented in fantasy stories. Pointing out that there’s an in-universe explanation for why this may be the case doesn’t solve the lack of representation. These stories are fiction, and you can add any explanation for why disabled people exist as easily as you can erase disability completely.
This video does a good job of explaining this some more: https://youtu.be/AxV8gAGmbtk?si=YRvXjpZv_YP9Z5sC
For what it’s worth, the reputation of the BrandonM comment on the Dropbox post is pretty overblown compared to what was actually written. The post highlighted some concerns that were legitimate in 2007. And the tone of the comments were supportive of dropbox – the poster acknowledged the feedback and offered use cases that still would lean towards Dropbox, and BrandonM responded that they made sense and wished them luck.