Many refineries were closed by oil companies with the intention to reduce supply and raise prices. Now there is a glut of crude, and they don't have the capacity to take advantage of the low crude cost / high refined product cost. https://books.google.ca/books?id=74brGsoymBoC&pg=PA35&lpg=PA...

Recently they have also been deferring maintenance to keep capacity of their refineries as high as possible and now failures are causing major shutdowns.