Why? The reason both streams are overcompressed is the same: cram more channels into the available bandwidth. Many people aren't as concerned as we are about PQ, and even fewer IMHO are concerned with AQ.
Why? Because the file size difference between hq sound and crappy sound is tiny relative to video. And I think most people who have worked in audio/video would agree that sound is more important. A video with poor sound is unwatchable.
I disagree that fewer people are concerned with audio quality and believe I could prove it in real life with a simple demonstration. Just because people don't talk about it doesn't mean they don't value good sound. It's the type of thing you don't notice, until you do.