As @adamhcaldwell stated the lower your hips the less ability to keep edge pressure which makes complete since and is the reason why standing taller in the transition is ideal. In addition to this, the further the ski is out in front of your COM during the transition regardless of straight legs or not, the more edge pressure you lose. So, you can have straight legs through the transition but if your ski is too far out in front of you it effectively is as if you were squatting through the transition. Jeff Rodgers was notorious for this into his 1,3,5 turn which is part of the reason why he always had huge turns on that side, his ski reached apex too soon as his body fell inside the line closer to the boat. When he got it right and stayed on top of his ski all the way out through the transition, he was pretty much unbeatable. If not for his superhuman abilities he would have never been as great as he was/is. In this picture even though his legs are relatively straight, his COM is not stacked over the ski which through the coming transition, will mimic lower hips.