I don’t understand why there isn’t higher demand for audio phones like there is for camera phones.
I agree that there should be demand for a large enough niche audience, but it won’t be even near the same demand as for good cameras.
For most people smartphone are their primary and usually only camera. And there are plenty of situations where you want to take a nice picture or video.
With audio the trend nowadays is wireless for the vast majority of people. And for that a build in DAC doesn’t really help at all.