What "people" are you talking about?
Sounds like some geek subculture, most people just want a hifi system and they use it until either it breaks or it doesn't fit their needs anymore (like, say, old receiver lacking HDMI inputs, whatever), then they throw it away like any other piece of consumer electronic goods.
My previous surround setup, I'd had it since 2003 and when I was done with it I put it back in the original box which I'd kept down in the basement storage room for all these years, stuck on an adhesive note that it was broken and in need of service, then placed it in the main corridor of my apartment block. It was gone inside of 15 minutes.
I can't imagine the second hand value for a regular amp or a set of speakers costing a few hundred $s being all that high, and if the amp then breaks you'd need specialist training to fix it (which very few people have) or it'll cost you more than the value of the device to have a repairman do it. If the spare parts are even available, mechanical switches and things of that nature may be proprietary and thus unobtainable. Same thing if you say, drop it and crack the front panel or something like that. Probably unfixable and not worth the expense even if it is.
