We are a large refinery source, we use lots of oil. It cost money to transport oil overseas. It always makes business to use it here first, if supply and demand are not out of sync, as currently exists in the Gulf Coast Light Sweet market.
Expecting the government to keep up with market changes would be foolish.
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?