Perhaps it has to do with the fact that she was never proud of the USA her entire life - until recently. But I'm going to take a wild guess and say the reason that Michelle Obama was booed by NASCAR America has more to do with this:
Obama's Great Depression
Boos? Her husband destroying the country the rest of us love in good times and bad will have that effect.
Michelle would do well to stay in Manhattan. The 1% there seem to appreciate her company.
But out here in the world? Message delivered.