Here's a stray thought about why Simon & Schuster may not have pushed unabridged audios when the technology was making them more efficient to produce.
If unabridged novels are bought by people as an alternative
to reading the hardcopy book, but the book sales are still respectable, is there a pressing need to put a finger in the dyke?
Yes, the abridged novels reacted to changing trends over the decades. They got longer and longer, and fewer in number, eventually only adapting hardcovers, moving to CD-format and cheaper narrators, and eventually drying up all together. But, in my own experience, I was a completist and only twice played the abridged audio before
reading the book ("Sarek" and "Stone and Anvil"), and then I had
to read the book.
Unabridged audios might attract new consumers who prefer not to read, but established fans are supposed to choose
audio or book, but not both?