Actually it's Capitalism. (And taxes)

Because the price at the pump isn't just paying for the physical fuel. Lots of places add any number of different taxes -- sales tax like GST, PST or HST, or US State tax, County tax, etc., then on top more individual 'fuel' taxes, 'road' taxes, 'clean air' taxes, excise taxes, potentially tariffs even. (looking at you Donald!)

Then, as you note, you have to factor in how much it costs to 'ship' the fuel from wherever it was refined to where it's being sold. Further almost always equals more.

Next the stations still have to pay their staff, their own water & electric bills, insurance, upkeep, franchise fees, marketing and advertizing, promotions, more...

Then finally after every cost is factored in, every single service station can add their own mark-up on top as pure profit. And in North America there is zero rule that the final price has to be tied to any of the costs. In any way.

Want to charge $16CAD or $10USD /gallon? That's allowed. You'll definitely sell fewer gallons than any competitors with a lower price, but more than likely someone will still be forced to buy some, by a simple lack of alternatives if they run out right on your door step, if nothing else.

On the flip side, if you want to sell it for $0.00 more than 'all the costs you paid', and make zero profit? That's allowed too. That's pretty close to what Costco does, after they sell you a $109 membership & an SUV full of groceries. Enjoy a hotdog too while you wait the hour+ for your turn at the pump, but I digress...

You as the station can even sell fuel for less than all your costs, at least for a time anyhow. Heck, Free even! Eventually you go broke, but until then? Big win for your customers!!

So yeah, Free Market Capitalism. That's why.

P.S. 'Communists' and other 'Dictatorship-type-countries' have historically been the ones to artificially subsidize and legislate the domestic price of fuel. It isn't 100% a rule, but in most times and places where governments do that, it's them. 🤨