You have it backwards because you're confusing muscle tone with size. A six pack has more to do with less fat than it does large muscles. Stronger bulkier beings generally have more fat and less muscle definition than a quicker agile being with a good diet. Have you ever seen a weightlifting competition? They really have little muscle definition, and almost look out of shape in comparison to a body builder, swimmer, or runner. It makes sense that the night elf female has a clearer muscle definition, especially on the stomach. An Orc, even in really good shape should be bulkier but less toned because raw strength like that comes with a layer of fat over the muscle.
It's for males but