Because oil is a commodity that the government doesn't control. Didn't you take economics?
Disruptions or even the fear of them in oil producing nations cause the price of oil to spike, which causes gas to go up. Harvesting requires oil for fuel, shipping the food to stores does as well, causing it to be more expensive to distribute. This sends wholesale prices companies pay for raw materials up, which in turn raises the prices of the finished product which is then shipped to stores, who jack up their prices in response. Rarely are prices reduced once the consumer gets over the sticker shock because even if it no longer takes an extra five cents to get each unit to the store they know we will pay the extra five cents.
In short, It's Capitalism.
SIMPLE : it's not in "their" best interest.
now why would they do that?.......tax payers are easily replaced......open the doors? & in they flow! ;-)