By keeping all your assets in the country where you live, you commit, ahead of time, to ratify whatever policy your home government might adopt, no matter how objectionable, unreasonable or pernicious that policy happens to be. If the next new mandate is "Register today to get a nail pounded into your head," you're already signed up.
Americans, by and large, run all their affairs within the confines of the US. The US economy is so large and so varied that it's easy to assume that everything you want to do with your wealth can be done without crossing any borders. And people in the US, like people anywhere, live with the habits and attitudes developed over generations. They're only human. In the case of Americans, those habits grew out of long experience with a government that was small and that generally practiced the rare virtue of following its own laws. In a happy exception to mankind's experience with rulers, there was little to fear from it.
Stay at home is still the norm for Americans, but it's a norm that is slowly fading. Every billion-dollar tick of the government debt clock, every expansion of the government's regulatory apparatus, every overreaching judicial decision made in the name of a compelling public need, every inversion of protection for citizens into license for the state and every intellectually tortured discovery of a new meaning in the Constitution's 4,400 old words leaves a few thousand more people wondering how prudent it is to consign all their eggs to a single national basket. Encounters with high-handed IRS agents and eager TSA gropers do nothing to ease that concern. And for those who listen thoughtfully, the messages from our designated leaders and their would-be replacements only hurry the dawning sense of unease.