I'm sort of shocked that they don't already have this.
My opinion is that they don't want the headaches that come along with it. You have to contract to have it done on tee shirts, hats, balls, etc. Then you have to stock these and take orders, redeem, ship etc.
In the past I think the British or US Open prizes were distributed by a third party. There are companies that happen this though and WGT could certainly work with one of them for order fulfillment and have a shop page on the site.