Prices in RPGs have never 'made sense' to me. But luckily I always end up with a bunch of gold endgame. I'm pretty sure the ratio is calculated based on a formula to 'balance' the game based on items/gold available to PCs. And not on what 'makes sense' if I were playing an economy simulator.
It's a bit simplistic, but it makes sense. A shop owner won't pay you what they sell it for because they have to make a living. Selling perfectly good weapons and armor you might expect it to get more like 80% of the value, but 50% hasn't proven problematic in the past 40+ years.
