Strength: orks are, on average, twice as strong as humans.
Reproduction: ork females rarely die in childbirth and usually have twins.
Height: orks can reach up to almost 8 feet tall.
Growth: ork children typically reach full size around 13.
Intelligence: The average ork and the average human are about the same but orks never go past that so you will never have a ork Einstein.
Longer life span: Orks die of old age typically in their mid-50s.
Psychology: Orks are slightly more competitive then humans and less cooperative.
Given these advantages (especially the strength and reproductive advantage) is there a reasonable explanation for why humans haven't gone the way of the Neanderthals?
Edit: They eat the same food but orks require more protein and calories.