Do you think monsters just wait around for adventurers to show up? Goblins are people too, and they don’t like getting a raw deal all the time. Players roll 3d6 six times and apply ability scores straight down, in order. You get what you get, and your class is randomly assigned. Are you a barbarian with a CON of 3? Tough noogies. A clumsy thief? A not-too-bright wizard? Welcome to life as a goblin. You still have to try to stop those adventurers, though.