Because if he wanted to do something, he would have done it by now. He's also not that extreme or that illogical if you compare him to others, like Kim jon il. Kim jon il is 100X's more looney than the leader of Iran and he has pretty much full nuclear capabilities if not now then soon enough. He's in the same boat, he DOES NOT want to throw his dictatorship away. What you have to see about these guys is that they have no grater love than themselves and their power. The mere thought of loosing this to them is terrifying. They simply use nukes as international scare tactic playing cards.
These men are fundies, but not straight jacket worthy candidates. They are simple disillusioned people in positions to abuse their power, and they love it and do not want to lose it.