Audio quality may be only one metric, but it is by far the most important. When shopping for headphones/iems you first listen to them and find the ones that sound how you like, then you compare on all other factors. I think most people who buy them do so because the marketing, not due to the experience. They know the brand and know they won't suck. Not that they are the best.
I doubt anyone I know cares about audio quality better than what airpods provide. What they care about is a device that works (I.e. pairs and has long battery life). Plus it has some neat features integrated with other Apple hardware, such as being able to listen to the audio from an Apple TV.
It isn’t by far the most important. I have numerous audiophile headphones which provide a better listening experience than AirPods, but I use AirPods almost all the time because they are with me when I need them.
"The best camera is the one you have with you" is a saying among photographers, and the same goes for headphones. Apple realised this a long time ago, and they sell both.
I, and I expect many others, mostly use them walking down the road, or around the house. And mostly for voice, not music, in my case. Audio quality certainly isn’t my main priority; comfort, battery life, and reliability are all far more important.
