[Water Warrior 2]

The key serves 2 purposes. One is for proper alignment of parts and Two..........it is the weakest link in the chain. It will shear off due to metal fatigue before something else lets go and causes major destruction. This is my opinion only but seems to make sense to me. The manufacturer could make everything absolutely indestructable but then you have a 250 GZ that weighs twice as much and costs a lot more too. The key is a sacrificial item to preserve the rest of the engine.
Luckily you only had to do some minor repairs rather than push home a bike with a grenaded engine. Look at the positive side of the repair. Could have been a lot worse.