Nice you mention transportation cost. At one time, transport costs were in and of themselves a form of tariff on goods from other countries competing for US markets and goods from US markets competing overseas. That's not longer nearly as much of a factor as it once was, especially in commodities shipped in purpose designed bulk carriers.
Shipping costs are obviously lower than refinery improvements or the industry would be fighting the tough battle of getting refineries in shape or built to handle the product they produce here rather than taking the politically easier to purchase export route.
Why fight the EPA, Quota monsters, liars for hire, special interest NGOs, both "F you, pay me" political parties, and all the other restraints on the free market here at home when you can sell opting out as "Free Trade" and "letting the free market work"? A few campaign donations to the right people and interest groups and you're out of the mess so who cares if it screws those who can't make the required donations ?
That is, who cares if it screws everyone who can't pay to play, after all, "I got mine, F you", right?
Why would any want to spend money to modify a refinery to use a more expensive oil? To raise prices in the US?
Where the refineries can be expanded economically, to use more oil, locally produced, to make more fuels to sell, that makes sense. But it also means more net export of refined products of the surplus.
Shipping costs are obviously lower than refinery improvements or the industry would be fighting the tough battle of getting refineries in shape or built to handle the product they produce here rather than taking the politically easier to purchase export route.
False premise. You also have to take into account we are already refining more than we use.