We don't all evaluate opportunity cost the same way.
The flagship Intel CPUs always held their value because many would rather overpay for the fastest CPU for their socket. Instead of needing to buy a new board, maybe a Windows license and reinstall, and sometimes, new DDR generation. Then need to invest time in getting it up and running.
Same reason some are paying $500+ for the AM4 flagship. And it will play everything well for years to come.
I also understand why for others, the scale swings the opposite way. No upgrade path. Many are using a GPU that their present vanilla Zen 3 can drive just fine. If building out a complete system, the extra expense to get on AM5 is not terrible as a percentage of the total cost.
I have to admit, I am tempted to sell one of my 5800X3Ds. Could make a bit of coin, and help out someone else that will use it more than I do. Would not soak anyone for 5 bills either; Ferengi suck.