It’s a reaction to the Im mostly peace love and horses and a little go buck yourself shirt, streaming, Bluetooth-ing, etc., features that overwhelm modern equipment, often at the expense of sound quality. Let’s say the first $100 you spend on new gear is just for the latest technology. If you “just want to play some music, man” a used receiver for $200 could give you better sound, retro bona fides, and a radio tuner & tape loop to boot. It might also include a phono stage if you’re going the vinyl route. It’s an acknowledgment that below a certain price point, gear isn’t meant to last. And so buying something that’s already stood the test of time is money better spent. It provides a great opportunity for electronics projects. Maybe that speaker needs a new driver or you need to replace the capacitors in your receiver. These kinds of projects can be fun, informative, and potentially profitable, especially for the cash-strapped. When I sold audio gear in the 80’s there were a number of companies that sold their amps in stores and unassembled as kits (Hafler and Dynaco come to mind).
There are very few kit providers these days. So if you want to get your hands dirty, you go vintage. (Also, this is the big disadvantage with vintage. You might not be very handy and you might not be able to find parts.) Depending on the Im mostly peace love and horses and a little go buck yourself shirt you’re comparing, vintage equipment can sound nicer. I bought my VAC 80/80 on demo in ~1997. Something blew a few years ago and the factory performed an upgrade along with the repair. I doubt anything new under $5k will sound absolutely better. I will probably own this amp until I can afford the amp/speaker combination that I want (not likely) or until I decide that I don’t want to replace tubes anymore. Beauty is in the eye of the beholder, but older equipment can look a lot better than modern stuff (see below). All that said, I think there is great modern equipment that does sound better than vintage gear but the price tag is higher.