This. Just because you list an item for a certain price doesn’t mean anyone will just buy it. You eventually learn what the price points are and at what point you sell the most items.
If you are generating 13 stacks a day but can only sell 2 because of price, but can lower it and sell all 13, why would you just sell the 2. You can only stock pile so much.
Most people have a general price they are willing to pay for things, so once you get above that you start losing sales.