I can tell you that it's not as simple as licensing issues, though those are a large part of it.
Each country has their own copyright rules and protectionist regulations which factor into things, and then there are union (SAG, SWG, AFM, etc. in the States, ACTRA in Canada, etc., etc.) considerations which have payment schedules for broadcasts in different countries, re-broadcasts, etc.
How it generally works is a TV program that is made in the US is meant primarily for a US audience - meaning how it makes its money is by how much advertising the network can sell around it domestically. That's a TV show's bread and butter right there. If a network can't sell enough advertising at home to cover the production costs of a show, it won't last very long.
Where licensing comes in is when the networks offer up their programming to foreign broadcasters - this is the gravy as it is often pure profit. But those licensing deals usually come with their own caveats in terms of broadcast times, repeats, digital broadcast, etc.
But the bottom line is that programming from countries outside of your own are regulated and still have to be bought and paid for so it's not quite as simple as "you should be able to watch a show across the globe all at the same time..."
