Isn't it simply because what you (or "we") understand as "hifi" simply isn't relevant to those of a younger generation? It's all about ease of access and short-term enjoyment now - preferably with a video component added. The "quality" is all about the story and production value - very little relevance to how it is reproduced (which will, of course, invariable be via a phone). Similarly, very few youngsters are buying into traditional video cameras or DSLRs - phones are perfectly "good enough" (and for 99% of purposes, they are...). Indeed, I'd be more surprised if the question was "why is the younger generation still buying hifi"?