It isn't about choosing DRM. Unless the DRM is obnoxious (video games often), then usually you don't even notice it. So it becomes a non-factor in your choice of audiobook store. However, when someone makes the rejection of DRM an ethical or moral issue, obviously even transparent DRM becomes important. The thing is that most people don't care.
Yep, the one driving factor in the mass adoption of any new technology, especially when it comes to media consumption, is convenience. All other factors, like quality, cost, or restrictions (like DRM or availability) are secondary. This has played out the same in every single format war, from Laser Disc, VHS, DVD, cassette, vinyl, MP3, torrents, and streaming services. If you can make something more convenient than what came before, you win.