Steve Danuser more or less admitted this in the lore interview of January 2019 (the one that everyone was hoping would be a Q&A but that turned out not to be).
“When you look back at things with Garrosh, the result of that didn’t really clean up some stuff. But it didn’t really fundamentally made Horde look at themselves and question themselves. So with Battle for Azeroth, let’s look at those things.”