Because the distribution rights probably belong to someone else in said countries. It's the same reason why some songs are available on iTunes in the US but curiously missing elsewhere.
So why don't they push the distributors to release the stuff at the same time? It's their content, it's not the distributor who complains about piracy and lost sales, the studios can just kick them out if they're not making any sales... Besides, there are many countries where they have literally no presence whatsoever and it's like they're actively trying to prevent it from building up (unlike Microsoft, which just let people pirate their stuff, then came in and said "actually, you need to pay for that" - in reference to Poland, Bulgaria, Hungary and Romania, where they successfully converted many companies and government agencies from pirates to paying customers)...
Because the distribution rights probably belong to someone else in said countries. It's the same reason why some songs are available on iTunes in the US but curiously missing elsewhere.