That's because your weighting of the bike in a corner isn't dependent on your CG. Yes, it'll affect your tip-in, but beyond that, it's irrelevant. Free-body diagrams will show that how your weight (where it is) works as if that weight were applied only at the contact points. So if you're weighting your outside pedal like you should be, the bike acts as if that amount of weight were sitting on that pedal, not at your body's CG. Small changes in BB drop does have a significant affect on the height of the pedal from the ground and how weight applied there affects cornering stability.