It’s totally about product cycles.
‘Economies of scale’ are a thing. Whatever range of parts are being fitted to a bazillion bike right now are cheap to produce because the lines can just run. This means they’re cheap to the OEM and bike industry, not quite so cheap to dealer/shop and slightly less cheap to you.
As a manufacturing company you want to make what sells, so you make most of what everyone is buying right now. hence the above situation. Excluding outliers like shops with huge stock that they don’t reprice, the further away from current ‘standard cooking’ parts you get, the bigger PITA for the mfr as they have to either changeover a line for a short run once in a while or start up a disused line for a short run once in a while. This is expensive. So, the ‘old’ part is expensive into the dealer network and hurts you even more.
It really doesn’t matter what people have in the garage. What matters is what the manufacturers are fitting, now, and how far away from that you are.
It’s not a unique situation to the bike industry, you see the same in the Computer world just to name one. Pick the type of memory your machine ten years ago used and look up a price for it. Then look up the price for memory for the latest and greatest. It’s probably a quarter of the price for the new, super fast part.
All part of our disposable, throwaway society… :/