Well unlike your ass, I appreciate the nuance of a good performance. But i know what you mean.
GPU time, while cheaper than a voice actor, is still a bit spendy though. And you then you also have the various copyright/licensing "issues" associated with AI content, companies may be a bit hesitant to go all in on producing books like that. Makes more sense for someone like Amazon/Audible and less sense for someone like spotify.
Besides, most audio books exist already so that really only applies to newer titles.