There are a couple reasons for this, but you should always do what works best for your body. In general, the fit from CF to the side seam is not where excess ease is found on a gaping waistband. You can check by pinching the CB until it fits closely to your body and checking the side seam location. If it’s centered, that tells you all the adjustments need to be done to the back. Also, the front generally doesn’t have darts, so it’s harder to remove excess width from that area. The side seam can only be curved in at the waist by a small amount before it starts getting distorted. When drafting, you always want to create contours with seams and darts instead of curving the sides on a woven pattern.