They are actually among the cheaper upgrade obsessions. Things like 286-386, 386-486 upgrades and PII overdrives are double the price usually. I think that's because there was a large overstock of them back in the day, in 96-97 they ended up priced higher still than a board swap upgrade with low end Pentium, so there was a lot unsold.
The hype period was overextended too because they were expected from soon after the Pentium original 5V version launched then didn't actually release until 1995. Due to a spec change, about a year's worth of "upgradeable to Pentium" 486 boards wouldn't actually work properly with it. So the people who craved it longest, those who had the earlier "POD upgradeable" boards, couldn't have it. So there is irony in that if they kept their original board/system or bought the exact board more recently, they still can't do it, so to "finally" use one they'd have to get another board. There's a bit of a narrow window only months wide where ppl could have had a 486 board that it will work on and socket 5 not appearing yet to be the mass market pentium, those buying 486 after that point even if it was pentium upgradeable probably placed their cravings into wanting a P90 or 100 but not affording it. Not that any of this nostalgia stuff is logical at all.
Maybe Intel didn't anticipate 5th/6th gen class competition and didn't think prices on that would get forced low and they would sell more POD. Buying one with your new 486 board or system would have been a strange choice due to pricing, and might only have been done by people owning high end VLB cards.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.