If you blow a hole in the side of a bus then the bus can come to a halt and the passengers disembark safely. Same story with a train.
If you blow a hole in the side of a plane, then no one can disembark until the plane lands, and the plane itself may simply disintegrate mid-air, killing everyone on board.
Same story if you fill the bus or train with toxic gas, or try to start shooting, or literally any other form of attempted mass casualty attack. Planes are uniquely different to all other modes of transportation because you cannot disembark them quickly and the default failure mode is everybody dies.
If you blow a hole in the side of a plane, then no one can disembark until the plane lands, and the plane itself may simply disintegrate mid-air, killing everyone on board.
Same story if you fill the bus or train with toxic gas, or try to start shooting, or literally any other form of attempted mass casualty attack. Planes are uniquely different to all other modes of transportation because you cannot disembark them quickly and the default failure mode is everybody dies.