In the 1960s and 1970s, every young person I knew, including myself, craved a stereo. (If I recall, we all called it a stereo and not a HiFi.) In college, and afterwards, as soon as we could afford it, a stereo was among the first things we purchased. It was one of those things that defined the so-called baby boom generation. The very large size of that young generation certainly also helped to fuel the rapid growth of the audio industry.
But IMO, what really drove this was the fascinating developments in new popular music during that same period. Most of that music was produced by small or independent recording companies. The big labels had lost control of new pop music sales, and scrambled to catch up. There was big money at stake. By the mid 1970s, much of the earlier momentum of the small and independent labels had been lost, accompanied by the maturing of the baby boom generation. There was less and less new and interesting music, and many baby boomers, myself included, had other things that occupied their time and money. The arrival of disco music, like a flu epidemic, put an end to the careers of many recording artists. Most of them had passed their prime any way. What remained by the late 1970s or early 1980s, had little resemblance to the 60s and earlier 70s, and the big music labels regained control of music production and sales.
They proceeded to ruin it by killing originality and raising prices. This happened at the same time as CDs and MTV emerged. I know I was interested in what new improvements CDs might bring, but I ignored them until the early 1990s mainly because I wasn’t much interested in new music. The next generation younger than mine, apparently was more interested in music videos than music itself without the video. I found most of that music uninteresting and largely ignored it. I thought I was getting older and my tastes had changed, but looking back, I think it was because the music and artists “manufactured” by the large recording companies was dull stuff.
Around the same time, the Sony Walkman first appeared, creating a new market for personal portable music of fairly good audio quality. The early Walkman played tape cassettes, but soon the Discman appeared. In the 1960s and 70s, audio played back from LPs or tape cassette recordings (after the appearance of Dolby noise reduction) was significantly better sounding than the only portable music of the time, AM (and later FM) radio. With the Walkman and Discman, this gap shrank. The later appearance of the iPod and the iPhone only continued this trend.
By the 1990s the thing most young people craved was not a stereo, but a computer. We are all familiar with how computers and the internet transfer of music files brought about the demise of the music industry. This came at a time when new music was significantly more expensive than in earlier years, but also at a time when new music lacked the widespread interest that had existed earlier. Besides, computers were not only becoming essential for communication, school, and work, but stereos were becoming more and more expensive. This certainly was not helped by the unfortunate trend of the audio industry to promote voodoo and snake oil as a way to increase profits.
Wow, I didn’t know I had this much to say! I guess I can summarize, what killed HiFi wasn’t the lack of quadrophonic sound, snake oil, or greed so much as Madonna and Michael Jackson and the big businesses that promoted them.