I think the error is assuming everyone in lycra on a road bike is out there pounding the pavement 10+ hours per week. Even Cat 3's don't need to train that much to be competitive racers. IME, without restricting calories through diet, if you want to burn enough calories to sustain weight loss it comes down to volume. At ~100 miles a week of cycling I didn't lose a pound. When I started ride at least 150 miles a week the weight fell off. One other variable is climate. If you live in a cold climate than winter, for most, means cutting back considerably on cycling volume which is bad for the waistline.