Probably because those Ogres are mercenaries, not slaves.
We don’t include Orcs from Orc Tribes in the old world. We enslave them, rob them of all their possessions and make them slaves. When we send them to battle they are only armed with what we give them.
But what is a choppa? It’s a big piece of metal on a stick. Anyone can make those, but only Orcs can wield them in true Orc form. Light armour, we give to them, yanno, if they behave.