In the U.K. we like America, we even have a 'special relationship' (according to our politicians, the fact is that no American politicians see it that way or mention the fact). However, do most people in the U.K. want to visit or live in the U.S.A.? No! Further into Europe I really doubt that the average French person would want to up sticks and move to the U.S.A.
If fleets of B-52's carpet bombed Europe with free U.S. passports, visas and one-way tickets to 'the land of the free, home of the brave' I very much doubt that there would be that much of a scramble to pick them up, hop on a plane and rush to the U.S.A. Sure, some would go, but even then, after a year or two they would want to return.
It has been a while since I have heard anything about floods of refugees wanting to leave Russia, so life there can't be all that bad.
What's to say that Snowden isn't actually enjoying life in Russia? His C.V. is rather impeccable and I doubt he will be struggling for work. He is almost certainly not without his female admirers too. He might just get used to knowing that the U.S.A. is off limits. He might also be able to be relaxed about personal security. He knows that if anything happens to him then it is pretty bad news for Uncle Sam even if it is a lone nutter that does the deed.
Okay his asylum status runs out in less than a year but how much does he really value a U.S. passport? Or for charges to be dropped against him? It is not that big a deal. Uncle Sam has no leverage here even if Americans don't see it that way.