The smaller the country it is, the less it has to lose, because in most cases small countries only have friendly regulations to offer as form of competition. By offering friendly regulations you're more likely to attract businesses looking to escape from the tyranny of countries such as US, China and Russia.
The US has its monetary policies it wants to protect at all cost, and I can't blame them for doing so. It must be frightening knowing that with Bitcoin there is a completely new type of financial system that potentially could render them obsolete.
At the end of the day, it has to be profitable for an exchange to settle in a certain country. Taxation wise and user wise Singapore seems to be a fairly crypto friendly country to settle in.