Because our Muslim President doesnt want us to.
He is just the latest on the scene. The Communists, which he is also, have been undermining America for more than 100 years. Stopping our oil exploration and production though has been a rather recent endeavor, no more than about 30 years when they discovered the environmental movement would be an excellent vehicle for destroying us. However, their patience has run out and they are now overtly trying to destroy us. Hopefully, with the Tea Party Movement we are about to turn the tide.