A new PAC ad says it's because of Paul's fidelity to the constitution:
Timothy Egan's thinks the troops are simply tired of war:
[I]f the overwhelming service support for Ron Paul is any indication, the grunts of American foreign policy are gun-shy about further engagement in “useless wars,” to use Dr. Paul’s term.
“It’s not a good sign when the people doing the fighting are saying, ‘Why are we here?’” said Glen Massie, a Marine Corps veteran who lives in Des Moines, Iowa, and is supporting Paul for president. “They realize they’re being utilized for other purposes — nation building and being world’s policeman — and it’s not what they signed up for.”
I doubt they're backing him because he's a foul racist.
The Dish 