Well obviously you did it because you saw the bad demographical situation the orcs are in, with everyone who wasn’t an ancient veteran like Saurfang and Drek’thar or young hotheads like Garrosh wiped out by the wars, and the campaign in Norhrend. This combined with the orcs killed in the seige of Orgrimmar meant that they were going to get even more desperate as time went on.
Having Kairoz convince Garrosh to go back to Draenor means that the orcs of the Horde gains their homeland back in some capacity, and a reasonably large population of the ‘good’ orcs from Draenor that might provide a calming influence.
You devious little shit.