On the other hand, catering to ignored niches is a good business plan. If you can own a small segment, you can make more money than uselessly going after the center of where your entrenched competitors are.
Once the niche is conquered, this can be used to go after the less nichy segments.
The problem is that this niche is not stereotypically a very well paying niche. The intersection of high earners and disabled people is quite small (and the intersection between lowest 20% of income earners and disabled is quite large)n So, there's not really a lot of money (if any) to be made by focusing solely on this niche.
That's why the ADA and various government laws came into existence - nobody was catering to the niche since it wasn't lucrative enough.
That may be good for one individual business, but not good for the segment of the population that's disabled.
For example: restaurants. Take a world where restaurants have to comply with ADA regulations versus a world where it's expected that someone coming up with a business plan for a restaurant that caters to the disabled. It's the difference between a world where the disabled can go to restaurants or where they can got to a restaurant.
I'm simply pointing out that if you'd like to imagine a world where the ADA doesn't exist perhaps you can help yourself to a $500 plane ticket and say fly to Japan or Europe. I was mainly responding to your hyperbolic statement that the disabled could go to "a restaurant".
You'll find that the disabled have plenty of options, it's definitely not the case that if you don't say enforce wheelchair accessibility for seating areas that there are no restaurants around to accommodate the disabled.
But you do get a lot of hole in the wall places of a type I simply haven't seen in the US, e.g. what would be a very small take-away restaurant in the US, but with a ceiling high enough to have an upstairs floor accessible through some very steep set of stairs to get to a seating area.
That's what I mean by society being poorer for it. It's not a choice between waiving a magic wand to make everything wonderful for the disabled or not. Complying with what amounts to onerous building codes can cost a lot, and often that cost is so high that the establishment isn't viable anymore.
In that same society, disabled individuals must pay $5,000 for a plane ticket, because only one airline will support them and space is at a premium. They are limited to a small handful of chain restaurants which charge three times the prices of your "hole in the wall" restaurants.
I'd much rather live in a society where I pay a small premium (even if that premium is the loss of a few restaurants) so that if my legs give out, I can continue to participate in society; not just a small portion of it.
Accommodating disabilities today is accommodating yourself in the future.
Once the niche is conquered, this can be used to go after the less nichy segments.
See "The Innovator's Dilemma" by Christensen