My dog is smaller than I am, but he runs faster. Why? Evolution. While his ancestors were roaming in packs and chasing down their prey, my ancestors were throwing feces at each other while figuring out how to use pointy sticks to kill things.
The "player races" evolved towards intelligence, at the cost of many of the advantages predatory creatures have: speed, natural armor, natural attacks, enhanced senses, that sort of thing. Equipment and magic make up for this discrepancy pretty easily, though.