First of all, I think you are mixing both young people and new audiophiles in the same bag and call them newbies. I am 40 and yet I am a newbie in audiophile world. I have no interest in pop or rock now. However, when I was 20, I couldn't care less about jazz and classical music and all I wanted to listen was heavy metal and rap.
And that brings me to specific answer to your question - I believe the main reason why you see more hi-fi users demand heavy lows is a dramatic shift in demographic profile of hi-fi community. Specifically, it becomes much younger than even 10-20 years ago. Why it becomes younger? Only one answer - the progress in technology makes hi-fi cheaper and available for everyone starting from birth (my 3 and 5-year old's are sleeping while listening hi-fi music every day).
Hi-fi used to be available for those with big wallets, usually older population that preferred classic, vocals, or jazz. Now it's not on a high-stream anymore, it's on the maintream, hi-fi is the ears of every teenager, it became the new low (like boombastics in the 80th). And those with big wallets - do they stay with the croud? No, they move UP - to high end. It's up there, where no 18-year old can reach, they relax and talk about highs and middles, NOT here at the new bottom which hi-fi has become.