Because you are only looking at WTI pricing and not the average price most refineries have to pay for oil. Keep in mind we import more oil than we produce ourselves.
The price of oil most commonly quoted is West Texas Intermediate delivered to Cushing, Oklahoma. That is a bottlenecked, landlocked point in the delivery system and below the average oil price.
When you look back at the high prices in 2008, WTI was a premium price to imported Brent and corresponding to other imported oil.
These days the WTI is often $20 bucks cheaper than most the oil refined in the US.
In short, comparing the WTI/Cushing price of oil vs gasoline from 2008 to now, is comparing a number that was higher to the average refinery price to one that is lower today. It is not a real comparison.
Too many people want to compare to the spike price that lasted a few hours in 2008. That is not a useful comparison. The average monthly price of oil bought by refineries reached $129/bbl in July of 2008, the average price of gasoline was 4.114/gal at that time.
U.S. Crude Oil Composite Acquisition Cost by Refiners
http://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=R0000____3&f=M
U.S. All Grades All Formulations Retail Gasoline Prices
http://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=EMM_EPM0_PTE_NUS_DPG&f=M
The latest monthly data is for August. $100.2/bbl for oil and $3.78/gal for gasoline. The margin is a bit larger than before, but there are more regulations and higher costs associated with refining today then there was in 2008. The labor costs are higher, maintenance cost are higher. But the ratio has not changed greatly.
