I'm a little bit curious about this. Where do all the hardware from the big tech giants usually go once they've upgraded?
I used (relatively) ancient servers (5-10 years in age) because their performance is completely adequate; they just use slightly more power. As a plus it's easy to buy spare parts, and they run on DDR3, so I'm not paying the current "RAM tax". I generally get such a server, max out its RAM, max out its CPUs and put it to work.
Some is sold on the used market; some is destroyed. There are plenty of used V100 and A100 available now for example.