There's nothing in the ADA (or any similar legislation) that says that all services ever created need to be accessible. Whether such legislation applies to you depends on a lot of factors, whether your software is used in workplaces, government and education being the most important (but not the only) ones.

Sometimes it's the organization that's only allowed to pick accessible software, not the developer that needs to make the software accessible. Sometimes it's okay to use inaccessible software as long as an accessible alternative exists and can be used by those who need it.

If someone cared enough to break accessibility this way, they could implement a switch that conditionally disables accessibility where legally permitted. I believe Kindle already lets publishers do this, come to think of it.