It takes excess calories to build muscle, but muscle is much slower than fat to come and go. The cards are simply stacked against you, the slightest error will result in fat gain. Bodybuilders do it in phases by leveraging the fact that muscle is slower to change. They go through a building phase and use a combination of intense cardio, calorie restriction and high protein intake to reduce body fat. You will loose some muscle, but the fat loss is much quicker than the muscle loss. The only way I know of to do both is by eating twice as much while working out four times as hard. This might turn out fine for a 22 year old, but the majority of people would just end up over-trained and loose both fat and muscle.