That hits the nail on the head. People use a mouse until they get tired of using a mouse and learn the shortcuts. One advantage of Premiere Pro is that you can take your time learning the shortcuts if you wish. Or, set them all to your liking right away.
Remember when you first got tired of using the mouse for Copy and Paste, and finally got around to memorizing Ctrl-C and Ctrl-V? Slowly but surely we learn our way around.
Except perhaps in AE where we learn from the great Brian Maffitt who mercilessly instills the shortcuts into our memory banks. (No joke, he is a tough task master, but there is none better.)