To be fair, goblins and orcs typically have a tribal structure while kobolds are stereotyped as the lizard-dog people version of mole rats with a dragon fetish and a particular obsessive nature about being subservient to said dragon. While they might not make sense from a mechanical point of view, they are best used as the endless mooks chopped through to get to the hot headed dragon that's been mucking up the surrounding towns in later level adventures.