I would think HiFi like many things is a subscribed idea. How one gets into it is a moment of awareness of such idea, accidentally or not, I got into it because my mate back in uni had his first "entry" Tannoy with Cambridge, I thought my pioneer sounded nothing special. My mate went to the same school with Stephan the bassist from Placebo, one day he was at his house, surprised being a rock star he was, listening to a Sony stereo system. It's like I'm a violinist because I started the study since I was kid, hence I became aware of classical music, and then made friends with other people listening to classical music. However the concept of Hifi does come after the concept of music. One gets into music first and then perhaps one point he/she starts to think that guitar solo at a mate's system sounds way more like in the room etc.
I think what makes today's youngsters uninterested in Hifi also is the music today has a "sound", which is produced such a way, blame it on Pro tool, Cubase etc, I recently discovered Aurora from Norway, fantastic singer song writer, sounds great through my system but I just kept thinking it is just too neat, reminds me of Bjork who I think came from older era with older software, but the thing is younger generation can pretty access to all these software and self record, produce and release, the amount of artists who do it has multiplied, I don't know many kids today actually listen to albums. Music fashion evolves pretty fast, if things sound good on Bluetooth speakers, there will be little fuss about listening equipment, plus let's face it, if you only listen to Rap, Metal or Pop, bluetooth is probably sufficient.
Last thing I can think of is the price of hifi is a joke today, simple.
You say much that is true, but hi-fi can be bought at relatively low cost - you can build a system or get an all in one for the price of an iPhone.