Don't forget the physics of holding the door.

With a wide, short door you have to hang it on the short side, and less space for hinges, which leads to large forces on the hinges.

A wide, tall door allows you to use more hinges, spread out, along a longer side and smaller forces on each hinge.

This makes even more sense with doors made with heavy materials, such as various metals. A heavy door needs more hinges, and a tall door has room for more hinges.

Multiple use, large and hard to break down in a siege, large enough to let plenty of traffic through of various sizes.