As soon as a championship is won, the players put on commemorative hats and the team starts selling championship merchandise. In order to have that merchandise on hand, both teams must make it in advance, which means a whole bunch of merchandise for the losing team very quickly becomes worthless. The clothing is shipped off to the impoverished of the Third World.
Of course, something like a "Patriots 19-0" t-shirt isn't worthless at all to a NY Giants fan. Aaron Kaplowitz journeyed to a remote village in Nicaragua, and managed to buy some merchandise from incredulous inhabitants. Here's the story, which I expect to be turned into a movie ASAP. Via. (Image via.)
There's actually some Patriots 19-0 merchandise on sale at eBay.