Which is a pity, but nonetheless.
Some are non-native English speakers, some have lisps or other articulation problems, some have other marks of fluency deficiencies, some have under- or over-dramatic intonation, etc.
And even if they're perfect voice actors, often their microphone setups are sub-par, and it comes through in the recording.
Frankly, these AI voices are now at a level where the few mistakes they make are easier to forgive than some of those issues from human readers.
That said, the final hurdle -- giving them the brains to know when to skip or resolve hiccups in the source material, such as typos, formatting issues, or text not intended to be read aloud -- is going to be very hard to overcome.
So, will your books be available with an audio section as a free encore in the future? :)
From Joyce's Ulysses (capitalization possibly wrong): "nes. yo."
Good luck with that!