Nobody considered a terrorist suicide by flying the plane into a building until it happened. So they made the doors lockable so that nothing passengers did cou

Nobody considered a terrorist suicide by flying the plane into a building until it happened. So they made the doors lockable so that nothing passengers did could get them into the cockpit. During that they obviously didn't think that any pilot would suicide the plane by flying it into the ground. All the while there is value in driving planes into the ground, it's an unwinnable solution.