I'm not sure if you've ever been in a building, but in case you haven't, I can assure you there's a lot that goes into their design and identity beyond the presence of a wheelchair ramp. Cars look identical because of consumer expectations, not because of the ozone resistance of their brake hoses.
Websites, however, can experience drastic swings in recurring revenue, brand loyalty, all from the addition or removal of a seemingly minor visual interface element. Design = Sales online. If compliance for brick and mortar stores moved out of the entryway and into the mandated height of display cases, counters, signage for colorblind patrons, and mandatory gluten free options there would be a deluge of lobbyists to stop it.
Building onto the other reply to your comment, I think you'd be surprised just how much accessibility regulation already exists that's just invisible to you. You also use highly accessible websites every day, you just don't notice.
You might also not be aware of how differently these regulations are applied depending on the type of product or service being offered and the nature of its provider. If you're hawking a web-app for designing charts, you will probably not be asked to stop supporting rainbow color-scales. Now, if you're an educational institution whose admissions tab is unnavigable to visually-impaired people...
To some degree, where its followed at all, where its enforced at all, and when its not convenient exceptions get made. That's kind of my point... If this becomes a crackdown there will be an equally large backlash.