It is interesting when you speak to someone outside of the US, they look at you funny if you mention your stock allocation is 100% US, or anything above 50% really. Everyone else seems to have a global focus when it comes to stock investments but Americans. To them, it's like we cherry picked 1 country out of 100 possibilities. Obviously some Americans feel different, but you can see this bias in things other than stocks. Americans typically only speak English, while folks outside the US typically speak more than 1 language. Americans watch US sports, but not popular int'l ones like soccer. We also can pick out more than 2 or 3 countries on a map, while int'l folks seem to have a broader knowledge of world history and geography.
FWIW I have an int'l allocation to stocks in my portfolios, but it is part of a tactical strategy so I could be 100% int'l or 100% US depending on which is doing better at the time. For instance, you would have been much better off investing internationally in the 2003-2007 bull market, however the 2009-2014 era has been dominated by the US.