Google Play regional problem - WHY?

Can anyone tell me why developers limit their apps to only the US and a few countries on Google Play?

I bascially CANNOT install any popular apps, such as temple run, bad piggies, angry birds star wars, ski safari......

I don't know why they do this, opening up will definitely increase their downloads and income. Right now they are forcing me to hunt around for a third party app store to get pirated (and therefore free) games with ads stuffed in.