It’s actually the opposite: our refineries are great at processing shale, and Texas is the best place to deal with Albertan shale oil as well (hence why they wanted keystone XL so badly). We also have enough clean crude that can mix with heavier dirtier crude to enable that to be processed (so Venezuela had to import American oil to process their own). The oil industry is weird.

One thing is that shale oil is expensive to extract and refine. It wasn’t until recently when prices rose again that it became profitable.