Not a partisan political thing. The NFL is considered a non-profit by the American government. Owning a franchise -- even a bad one -- is a license to print money. The NFL owners have a vested interest in making nice to whoever is in the White House. Had Trump lost, the same amount of money would have gone to Clinton's Inaug.
Oh, if you're English and wondering why so much money is devoted to this event, it's because no tax money is spent for the balls and concerts related to it. It's all paid for by contributions.