Because, in the United States, the NSA and friends need to jump through the FISC hoops to listen in to your e-mail, cloud data transfers, phone calls, whatever. If you're doing any of the above to someone or some site outside of the US, any of your communications are pretty much fair game.
Let's step back for a moment. What is the NSA's job? Since Harry Truman set it up back in 1952 the NSA's job is to monitor foreign communications, whether it is electronic intelligence (ELINT) or signal intelligence (SIGINT). Update it to 2013 and the NSA's job is still tracking foreign communications. These can be either from one country to another, say Russia to China, or from someone in the US to another country.
It's always been this way. The NSA is a foreign intelligence agency. This is what they do for a living. Always have, always will.
There is nothing really new in what Snowden revealed to anyone who'd bothered to read the books of James Bamford. Bamford spelling all this out starting with his first book in 1983, The Puzzle Palace. The NSA is doing exactly what its mission has always been.
So, if you think for one second that moving your data out of the US, or keeping it out of the US will somehow make your information safer, think again. By doing so you actually make it more likely that the NSA will have access to it.