> there really is no reason for even mom and pop sites to not provide even a base level of accessibility
Because it costs money to do so, and sometimes mom and pop sites are barely scraping by to begin with. It's also their prerogative to make the content accessible or inaccessible to whomever they see fit - it's their loss if someone cannot buy their product, but it's also their choice to accept that loss. I think it sets a dangerous precedent to make them legally obliged to make their content available in a specific way.
The United States has already decided that businesses in general (ie. brick & mortar stores) do not have the prerogative to make their content accessible or inaccessible to whomever they see fit. Including websites makes perfect sense.
Only 3% of the US is visually impaired, and often poorer than average due to disability, so for the vast majority of individual businesses, ignoring them would be less than a rounding error in revenue, and therefore warrant no consideration of accessibility. But the point of a society is to decide collectively upon certain moral imperatives that are deemed so fundamental to our collective identity as to take precedence over Randian self-interest, righteous indignation about "muh freedumb" and "don't tread on me" notwithstanding. One of those moral imperatives in the US is the protection of the rights of vulnerable minority classes so that we don't become a caste-based society where the circumstances of your birth (or unfortunate mishap) can indelibly decide your fate by limiting your access to society. This is actually MORE meritocratic than the alternative, and so I think, upon careful consideration, you may find that it dovetails nicely with even extreme Libertarianism.
Because it costs money to do so, and sometimes mom and pop sites are barely scraping by to begin with. It's also their prerogative to make the content accessible or inaccessible to whomever they see fit - it's their loss if someone cannot buy their product, but it's also their choice to accept that loss. I think it sets a dangerous precedent to make them legally obliged to make their content available in a specific way.