> but I don't know a single person who engages with them in that solitary way,

We exist. You won't know because it's solitary. You have to ask, and I doubt you've asked people specifically if they "engage with them" in that way.

I also think it depends on what you are reading. I read for enjoyment using audio books. I read to learn using real books. If you equate the two and assume someone using audio books is using them for non-fiction to learn something, I really think you are out of touch.