Originally Posted by Phobia
Because if the price on something goes up while it's in stock then you just added money in your wallet - just like if the price goes down while you're holding a bunch of product then you get screwed. Win some, lose some. The idea of being a good businessman is to win more than you lose. The gas stations themselves aren't to blame for the patterns questioned in the OP.
Your post talks about prices moving up and down, but the focus here is on why the rate of price change (price acceleration) is different when dealing with the same product.