Can you imagine 30,000 people controlling the UK? It wouldn't make any logistical sense. It would be something akin to 10 people occupying each town and city. By contrast the UK has somewhere around 130,000 police officers. The police are useless now, but imagine if you cut them to a quarter and asked them to maintain control. You sense that the country would fall to the masses. People are being asked to suspend a lot of reality with the Middle East. The 100,000 Yazidi turned out to be only a fraction of the number.