Sorry, wasn't sure where to put it. Your observation is appreciated. Most audio narrators are great at it, but a few of them are terrible. I could never hope to match Scott Brick at reading thrillers, but I beat the hell out of Roy Dotrice any day reading A Dance With Dragons. That was one of the most annoying audio productions I've ever listened to, had to keep going back over passages because I couldn't understand him. So I read some passages myself and taped them on the pocket recorder I use for my writing thoughts. At least I thought I was an improvement...
Heehee...so funny how opinions vary. I LOOOOVE Dotrice in all the ASOIAF books, and I think Scott Brick, while he speaks clearly all the time, often sounds smarmy or condescending, even when the text doesn't call for it. (He's still pretty good in my book, though.)
As for your question, I do have a bit of an answer for you, since I looked into this myself once. I was told I should develop a good "reel" of reading books. Get at least one good nonfiction piece in there, and a few fiction pieces from various genres. Try to adapt your presentation to the genre/book, and select material that shows a range of what you're capable of. Keep each segment of your reel to 2 - 3 minutes.
You'll also want to develop a resume that shows your talents as a performer. If you have acting experience, that is extremely useful. Radio presentation? Run a popular podcast? Member of Toastmasters? Anything that shows you have experience in making entertaining presentations will help. Looking for opportunities to work as a voice actor will help you get into audiobook narration.
Then, when you have a good resume and a good reel, approach the various audiobook companies and ask if you can submit your reel for them to keep on file. Don't expect them to have actual openings -- it's rare for them to have an immediate need for narrators. But they'll have you on file, and if they like your reel they'll eventually start assigning you to books. Once you get one job, the rest usually follow quickly if you've done a good job.
Of course, as always, if you know somebody in the company your chances of getting work increase dramatically!
Good luck...it's still something I'm considering. I might release my own self-published book as a podiobook and see whether it's popular at all, and if it is, I may try to leverage that into a way into the professional narration world.