Layman: skeletal muscles are expensive to maintain in terms of caloric and protein/water intake, and larger muscles are less efficient at dumping the heat that

Layman: skeletal muscles are expensive to maintain in terms of caloric and protein/water intake, and larger muscles are less efficient at dumping the heat that their use generates because volume increases faster than exposed surface area with muscular hypertrophy. If food and body temperature regulation were more immediate concerns than violent conflict, then the ability to gas out your opponent was probably less influential.