Mostly has to do with the fact that the rules need to be filtered through a lawyer to avoid them being sued or penalized. Doubtfully that is going to be a single one either due to multiple languages. Some places require the rules to be registered with a gov agency. And if local rules say to run it you also need to include translations of the rules in Derp Derp and Herpty Derp you need to pay to have it translated else you are breaking the law running it there. The fun really starts when you have places that require a bond to be put down for the prizes monetary value. Random places require taxes to be paid on the prizes value also. So yea. Multiply that by all the state/countries and it becomes a huge mess running it through legal. Easier to just start skipping places with costly rules. (Ex: Some states in the USA get nuked by the "Offer void where prohibited." phrase in the rules.)

I've no doubt that it costs them more to run a contest then the actual prizes value.

PS: Tagging a virtual item with 'No monetary value.' only works in some countries. So its not even safe to offer a virtual scarf to everyone else not eligible for the signed prints.