Remember this analogy: You haul aluminum cans to your local scrap yard. Let's assume that the yard pays $0.75/pound for them and they are 20 minutes from your house. If you haul a small bag containing one pound of cans, you're only going to get $0.75. The scrap yard does not pay you for bringing them in, just for the cans themselves. On the other hand, you crush your cans and on top of that, you collect cans from your neighbors and once a week, you walk a couple miles along the road and pick up any cans you find. Let's say this brings you to 20 pounds of cans collected for a month. That will be $15 in your pocket. The amount of gas burned is the same, the difference is the number of pounds of cans you bring in.