Let's suppose Yogi and Boo-Boo jump out of the thicket,,,
Yogi chomps down on your left arm so you only have your right hand to use,,,
Do you really want to be fumbling with your thumb for the hammer before you can shoot?
I never fumble with the hammer. I cock the danged thing, and then shoot the gun. In fact, I've done it so much that it's pretty much done now without thinking about it.
Motor-muscle-memory is a wonderful thing when you've practiced with your firearm enough to know how it works.
Daryl