Firing voice actors is not great. Replacing human-narrated audio with AI narrated audio is not great.

But the coverage of audiobooks is… also not great? Of the books I've purchased recently, maybe 30% or less have audiobooks? What if I want to listen to an obscure book? Should I be paying a human narrator to narrate my personal library?

The copyright holders are incentivized to make money. It does not make financial sense to pay humans to narrate their entire catalog. As long as they're the only ones allowed to distribute derivative works, we're kind of in a pickle.