GW orcs are biological anomalies that exist fully out of a need for selling toys that kill each other, D&D orcs are actually playable so saying they're brainless becomes much too limiting to players. Orc is basically a generic word that means "monstrous creature" different settings have different definitions of what an orc is supposed to be. Hell, even the guy who created the modern orcs explicitly had scenes that showed them as having thoughts and emotions.