This does not really make sense, it would be perfectly fine if two products existed, a cheap inaccessible captcha and a more expensive perfectly accessible one with companies offering both of them to users.
That is not happening in what I described. A webpage could decide to offer the cheapest working captcha as a default with a "Are you using assistive technologies?" / "Do you need help?" link to a more accessible service.
I don't think that is will be common in the wild, but it is an argument against regulating captcha providers rather than websites.
