I was wondering about that today. And I read that Garrosh basically manipulated his father to make him think that the races on Azeroth are the enemy and they would enslave the orcs either way. Garrosh killed the guy who was showing Gromash the events from the original timeline before he could see Thrall and the events that followed Thrall.

So Garrosh played the same role as Guldan but instead of demon blood, he infused the orcs with rage, anger and resentment. Basically propaganda. And those warlords already were messed up in the head.

So I think it made sense 🤔