Audio has been around since, I suppose, the spoken language. The difference now is distribution and availability. Audiobooks, podcasts, smart phones, voice controlled home speaker systems, connected cars, and who knows what will come next.
I'm an audio guy. I like headphones in, walk in the woods with Pepper, and lay those decibels on me. But it's not always...
It's just so easy. It's probably harder to not do it.
This is where things can get exciting with your book as a podcast as opposed to (or in addition to) an audiobook.