• Commands come in sequences. Having a command mode allows commands with fewer keystrokes and fewer modifier keys to make you more efficient. Also, move away less from the touch typing homerow.
• Commands are mnemonic. For example, z for folding...
Why hjkl? Touch typing homerow. Of that, h is left, l is right. The shape j goes down, k goes up. I don't remember specifically what hjkl do, I just remember that the whole editor is mnemonic. That way I remember more with less.
To see the limits of the success, look at the desktops. The battle is still going on. It's not only about software technology.