They're not excluding them on purpose or to irritate you. It's legal issues, and if those legal issues are resolved, the coverage area can increase. until then, they can only do it where the law allows them to. You really don't have any idea how hard it is to run a contest across multiple countries, do you?
Generally, it's only an issue when real monetary/physical prizes are involved. It's usually not a problem for in-game item rewards.