Because OPEC and other Oil Producing Nations control a large part of the supply. When they want prices to go up, the spicket gets turned off. When there is a glut (like you saw last year when the Pandemic hit) prices collapse. We are theoretically not dependent on foreign oil but it's a commodity that goes to the highest bidder. Canada produces enough oil for the country and look at their gas prices (about $5 a gallon). Many factors affect the price of gas over time (including inflation) but you will see drastic ups and downs based on supply and demand. Why would Saudi Arabia sell cheap oil if they can sell less and make more money?