Because when the gov't steps in it defeats the purpose of a free market economy. What would happen is that the gov't would create a gasoline subsidy. When this happens that creates a unlimited demand for gasoline. Then to counter that, they ration gas. So basically what happens is we see prices of $5/gallon and only allowed to get 20 gallons of gas per week per family. Do you really want that?
Also, you do realize the gas companies are paying corporate taxes and creating jobs?
Gas companies also make around 9.5% of the price of a gallon of gas, so about $.095 per $1 of gas sold. If you owned your own company and I as the government stepped in and said "sir, you are making too much money, you are ordered to reduce your profit for $.09 per $1 to $.04 per gallon" how would you feel about that?