That is a childishly simplistic understanding of how free markets work. There is no way a retail business would be established to service the needs of 2% of the population who are wheelchair users for example, when they could easily make their stores considerably more efficient by making the aisles a little narrower.
Slow down there, you're going to need more evidence than that to claim that an underserved segment of the population isn't an attractive commercial target.
I agree that wheelchair users might be comparatively expensive customers, but if that 2% stat is correct they would be profitable to someone. A business with 2% of the market as a captive audience is going to be profitable.
Honestly, I think the claim that the free market would solve this is so outlandish that the burden of proof is on those who believe it.
Maybe, just maybe, in a dense population centre like London their needs would be met by a few specialist 'accessable' stores. But what about some rural town of a few thousand people?
So disabled people don't get an automatic job, say. But an employer can't just decide not interview someone because "it's inconvenient to interview you due to your disability".
Another: It's not acceptable to say "sorry we can't interview you if you can't climb stairs, because there is a staircase between our interview room and the downstairs offices", because there is a reasonable accomodation possible, namely interviewing in a different room.
A shop is required to make reasonable accomodations, such as provide an entry ramp if that makes sense, and a wheelchair compatible toilet if that makes sense (i.e. it has other toilets).
That prevents shops from saying "we don't care about the 2% so we can't be bothered with a ramp even though the cost is negligable to us".
On the other hand, reasonable is relative. An organisation with no funds would not be required to do the same things as an organisation with plenty of funds. A club open to the public is expected to do more than a private gathering of people where nobody in the group has particular needs. And accomodation doesn't always have to be pre-emptive. For a public facility, anticipating needs of a broad spectrum people is expectecd, but for a small, private workplace it may suffice to react to the particular needs of individual people as needed.
(Note, disability is complicated because there are so many kinds, many of them invisible but cause much difficulty for the persons affected, and people without experience do not recognise the signs. I've used wheelchair here because everyone recognises that, but even with those, a lot of people seem to not understand that if a person can stand up and walk a bit, it doesn't mean they don't need a wheelchair.)
Whether it's the kind of discrimination the store is obliged to deal with is going to come down to principles of reasonable accomodation.
So, say you had an extremely boutique store up some rickety stairs, where the way it's used is you go up the stairs and meet the chef who will take your order for a wedding cake and you can collect the cake next week.
I would expect, in that case, if the chef is willing to meet you at your home or another place with a menu of options and discuss your order, and then have it delivered next week, that would meet the bar of reasonable accomodation for someone who couldn't use the rickety stairs.
On the other hand, a large grocery store, where browsing the goods is part of the experience and is also significant to product discovery, and maybe pricing and access to better fresh ingredients and different bargains, and where the only obstacle is that the store does not replace one door type with another that a wheelchair user can enter, and the store can reasonably afford the cost, that is clearly inadequate of the store; they have no good excuse and could reasonably accomodate by changing that door.
On another hand, the same large grocery store may find it difficult to accomodate people who cannot tolerate bright illumination (that other people need, to see clearly), and large numbers of people moving around them. In that case, it is not at all obvious that the store can do much to accomodate. I would expect that if the store also provides online ordering with delivery, that it has performed reasonable accomodation for that situation.
I bet most businesses would make their stores accessible (within reason) since you need room in isles for carts, etc.
It isn't that outlandish that the market will sort it all out. I doubt anyone is going to be unhappy if business get a bit of a prod to remind them that wheelchairs exist, but the idea a free market would ignore 2% of their potential customers is just not true. Greedy capitalists have incentives to be thorough; 2% of the market changing hands is enough to get the attention of any CEO.
Most businesses would notice 2% of their customers disappearing, let alone 2% of the broader market.
That is true, but it most likely leaves wheelchair users paying a premium on goods and services for the privilege of even being able to enter the establishment, and probably having a smaller selection of lower quality to choose from to boot.
That is what generally happens with captive markets, you know.
It wouldn't be the only obstacle. Let's take wheelchair-accessible parking spots for example. We have to convince the store that sacrificing regular-sized parking spots (and the ones closest to the store, at that) in order to make room for a smaller number of larger parking spots that are reserved for 2% of their customers (and not exactly the most profitable 2%, either) is a reasonable accommodation.
Bear in mind that some of those spots we're asking them to convert might already be reserved for the store manager, some senior employees, and the employee-of-the-month as perks, rather than for customers. You will have a lot of convincing to do, and should expect significant pushback from the local chamber of commerce.