This is basically the same as the sad affair of enterprise software. The vast majority of that industry is actively bad. Not just not good, but actively bad.
Do you think the quality of the alternatives might be related to the fact that Amazon/Audible is strangling all competitors out of existence with their exclusivity agreements?
Imagine if an audiobook competitor popped up that's a 10x better experience for customers and authors. They'd starve out of existence without major VC backing because even though they're better, they can't bring the sales volume that Audible can, so customers choose the worse experience on Audible with the exclusivity agreement because the total earnings are higher.
Long-term, that's a worse ecosystem for everyone except for Audible.
This isn't even that controversial of a take. Netflix doesn't offer a ton of the things I used to be able to get in DVD from them, because the publishing houses have very high demands on licensing fees.
(Also disclaimer, I work at Amazon but not at audible)
This isn't because Audible is head-and-shoulders above the competition either. They aren't. They just won the game of Monopoly[0].
[0] Someone should turn on house rules. Or - oooh maybe we could play the unused co-op mode