Have you ever wondered how some spaces, like talking book and Braille libraries or nonprofit groups like Learning Ally are able to produce audiobooks of everything from public domain books to textbooks to current bestsellers?
Well, some forward-thinking infovore in the mid-nineties realized that not everybody can work with print books, and so the Chafee Amendment was enacted to allow authorized (often nonprofit) entities to create versions in other media so readers who need accommodations have access to those books. This includes audiobooks, large print, and braille books that will be made available in noncommercial situations.
One of the unexpected side effects of this provision is that electronically distributed media cannot be locked down in such a way that it cannot interact with screen readers, captioning, or other adaptive tools. The idea here is to keep text-based information as available as possible, regardless of a reader's situation.
The need to make print materials accessible to those who need accommodations is so pervasive that in 2013, the Marrakesh VIP Treaty was enacted to provide a protection similar to our Chafee Amendment across international problications.
While publishers are catching on and trying to have audiobooks ready for print books expected to be in high or medium demand at the time the print book is released, they are commercial endeavors and therefore don't qualify for the provision.