If the internet is international and doesn’t have boundaries, why restrict by region?

It doesn't restrict it. They just happened to have categorised them like that at this stage. Perhaps they'll eventually split them into plugin developers, theme developers.

And why is WordPress the only Automattic product handled?

Perhaps add bbPress and BuddyPress developers to the list categories I mentioned above.

I'm guessing this is very much in the testing phase right now and more features will be added later.