Probably the general [[w:c:wow:#|lore]] reason that [[w:c:wow:#|orc]]s don't have a [[w:c:wow:#|paladin]] class available is that the standard in-game, playable green-skinned orc is supposedly a [[w:c:wow:#|mag'har]], brown-skinned orc that was corrupted in the past by demonic [[w:c:wow:#|fel]] magic. Since the source of a paladin's power is supposedly from the [[w:c:wow:#|Holy light]], it would seem an orc with the remnants of fel energies would make them incompatible.