Nostalgia.
He’s too fond of Orcs for me to fully trust him and whilst I admittedly do not know how much of a hand he had in such matters, I am still bitterly displeased that characters such as Kael’thas and Lady Vashj were squandered and unceremoniously killed off.
I also worry that he may have grown bored of Orcs as well as the Horde and shifted over his love and attention to Anduin instead of Thrall.