Because France would be considered as even more lunatic than it is today if France left, by both the US and other NATO members. But if the US decide to leave NATO, that will provide France with an excellent opportunity.
Not that this is the opinion of my governments, not mine. I love NATO and I absolutely want it to keep working. Who knows, even Russia can become a danger again if Europe is left alone.
It did? Really? Poof, just like that? Then how come French Jews have left or are leaving France? Because of your sucking up to your Islamic base and ignoring or outright denying anti-semitism exists in France starting with Chirac, you're driving Jews out of France--at least the ones that didn't die when the French turned thousands of Jews over to the Nazis in WWII. Your country is openly hostile towards Jews, denying it exists makes you a liar.
And I'm still waiting for you to source the list of "30 years of US vetoes at UN," most of which are for Israel. http://www.freerepublic.com/focus/news/859716/posts