[mdaniel]

While I find your explanation plausible, who has the muscle memory to press "g", "c", "c", spacebar, lift hand to numpad, "1", "6(no 3 sire!)", hand back to home row?

[jwiz]

To be fair, you can be typing "gcc" with the left hand, while the right hand moves to the numpad.

Efficiency.

[mrcarruthers]

It's faster for me than looking down to figure out where the numbers are on the top row

[abhibeckert]

If you used the top row more often, you wouldn't need to look down...

[bdhcuidbebe]

I would use both my hands