Because it's awkward I'd assume, and that space between the ring and the middle finger is hard to strech between two frets on a fast run. I'm working on stretching and stregthening exercises. Do you mean to say that Malmsteen doesn't use 4 fingers in his runs? Because I'd much rather not - I'm beating the crap out of my pinky every day to bring it up to speed. ... Actually now that I try it, it isn't so bad.