The problem is that sign languages are languages, and creating a universal sign language would much of the same problems as creating a universal spoken language.
First, you have to convince everyone that your language is better than theirs. Then... well, really that's the biggest step.
This isn't like a Morse Code or something, where it's simply a matter of governments and industries getting together to agree on some standard protocol. Sign languages are living human languages, with people who have been speaking all of their lives.
I'm fairly certain that the languages weren't designed specifically to separate people based on their place of birth. They are different because they have their origins in different deaf cultural movements in separate places.