Different countries, different pricing.
In my country, for example, the "old" Playstation 3 is still going for five hundred dollars. PS 4? Floating around the thousand dollars. I can, and did, buy me enough good parts to build me a sort-of-updated PC. If I could get enough to buy all three "big" consoles each time they decide to update, I would instead build a computer which could run games from all three instead.