Why was the ancient Egyptian lock key shaped like a large wooden bar?

The ancient Egyptian lock key was shaped like a large wooden bar because of its specific mechanical function within the pin tumbler system.

In this design, the lock consists of a large wooden bolt that secures the door, featuring a series of holes in its upper surface. An assembly attached to the door holds wooden pins that drop into these holes to grip and lock the bolt. The key is designed with upright pegs that correspond exactly to the arrangement of these holes and pins. When the key is inserted into the keyhole beneath the pins, it is lifted upward; the pegs push the pins out of the bolt, clearing the mechanism and allowing the bolt to be slid back.1