How about this: they ought to provide reasonable accommodations.

As far as I can tell most, if not all, of the chipsets used in ereaders are capable of audio output. The vendors are simply choosing not to expose this functionality to the user. There are also FLOSS TTS options out there. Given that these vendors are already using FLOSS code in their devices, adding one more component shouldn't be an issue.

As far as I can tell most, if not all, of the chipsets provide USB host mode. This can be used to interface to external braille and TTS devices if the appropriate code is added to the system. I'm fairly certain that there FLOSS code that handles part of this, so it shouldn't be very burdensome. The USB host mode can also be used to add special input devices as an alternative to touch displays for people with limited mobility.

As far as I can tell most, if not all, ereaders can enlarge fonts and change the fonts to better suit people with low vision. That is great, except it has to be extended from the ebook viewer to the user interface.

There is a lot of low hanging fruit when it comes down to accessibility. I cannot think of a good reason why businesses shouldn't be obligated to address that functionality when it reflects the intended function of the device.