Not that the books give a good excuse for this storyline anyway. Thrall promotes a hot-headed, inexperienced, emo orc to leader of the Horde, AFTER he tried to kill Thrall once already. Pretty much first thing he does as Warchief is kill Thrall's BFF Cairne, and Thrall is cool with it and goes off to Outland to make brown babies. That was the 'Cataclysm' novel.
Fast forward in Garrosh's term as Warchief, and surprise surprise he has been a bad boy. Seized the power of an Old God's heart in an attempt to annihilate both Horde and Alliance, plus pandas. AND NOBODY GIVES ENOUGH OF A FUCK TO KILL HIM WHEN THEY GET THE CHANCE. The ONLY possible reason he was allowed to live at the end of Pandaria was to give him a chance to escape and set up the Iron Horde nonsense.
Fast forward in Garrosh's term as Warchief, and surprise surprise he has been a bad boy. Seized the power of an Old God's heart in an attempt to annihilate both Horde and Alliance, plus pandas. AND NOBODY GIVES ENOUGH OF A FUCK TO KILL HIM WHEN THEY GET THE CHANCE. The ONLY possible reason he was allowed to live at the end of Pandaria was to give him a chance to escape and set up the Iron Horde nonsense.