Neither can most planes given the cockpit is sealed and locked. I suppose one could strategically try to take it down over a populated area, but that doesn't really seem reliable. The truth of the matter is that people can smuggle bombs onto aeroplanes relatively easily, and you don't see many blowing up. And it's not even entirely clear that planes can always take out buildings. The twin towers only collapsed because of the slow burn of jet fuel heating and weakening the structure. The impact alone wouldn't have been enough.