I write books and then convert some of them to audio format.
When writing the books, I give little consideration to the conversion to audio. I select a perspective (1st person, 3rd person, etc.) that best suits the story as I want it to appear in a readers' mind. I don't change perspectives, so there is typically only a single voice narrating the tale.
That isn't to say that there isn't dialogue by both males and females, but that dialogue is still presented by a singular voice throughout the story. Someone, either one of the characters, or an omniscient third party is essentially reading the story to the listener when it is converted to audio.
I realize that my approach is different than creating an audio "play", where different characters need to have a different voice. I don't consider that an audiobook.