Who designed safe keys?

I was back at work today, and I thought i'd measure just how much unnecessary extra steel I'm carrying around in my pocket. The key is 6 inches long...yet it sticks out 2 and a half inches even when it's fully in the lock as the above picture indicates. So who decided the key needed to be so big and why? It could literally be half the size and still function properly.

The best reason I could come up with is that they also invented belts and needed to sell a few more so they thought they'd make keys pointlessly heavier to produce more demand. Or is there an actual reason that I've missed?