If they're going to blow something up, why not a bus or a train or a bridge or a cruise boat or something? There's not so many people on an airplane that it's l

If they're going to blow something up, why not a bus or a train or a bridge or a cruise boat or something? There's not so many people on an airplane that it's like it's your only opportunity to kill a lot of people. The only (rational) reason I can imagine that makes planes different is that you can use it as a missile to attack a larger target.