Originally Posted by
Super Dickmann
It's one of those things that's hard to cover because of the overlap of out of story and in story reasons for it. Out of story, the reasoning for the Iron Horde not establishing their control over Draenor before attacking Azeroth is a combination of the expansion being dumpstered and them redoing a ton of zones after the case to avoid 'orc fatigue'. In the original version of Warlords, which you can see parts of in the Mag'har scenario Gorgrond was entirely industrial and the Grimrail criss-crossed the entire zone and went as far as Shattrath, getting across how logistically advanced the Iron Horde was. You can get bits of that from its current unchanged description which makes no sense with the layout of the zone or the progress of the story. Likewise, places like Elodor were already sacked by the Iron Horde, Kargath was a much bigger part of Arak and Blackhand had his own role. To go with that, their invasion was also more successful - they got past the Swamp of Sorrows and into Searing Gorge with the Kor'kron position in Blasted Lands swapping sides. That's why Zaela's able to go through and set up her doomsday device in UBRS. Other bits, like for instance the Highmaul story around Mar'gok implies the Iron Horde is a lot more advanced than we see, using things like automated crawlers, and that Highmaul is a complete client state. The situation around how the Blackfuse even got there and if it was before or after the time portal was also left as a total loose end when they cut the Chronal Spire and infinite dragon involvement.
The in-story reasoning that we're stuck with is that Garrosh was so fixated on going after Azeroth that he went in half-cocked and didn't care about suppressing Draenor . He has to dissuade his dad from killing off the ogres, but is just as short-sighted as he is and so his invasion mostly ends up as a failure. Grom himself is an albatross around the neck of the Iron Horde with Blackhand being vastly more competent as a tactician and the Foundry being the heart of their war effort. It's not a bad story beat that Garrosh's invasion plan ends up being undone by his main faults - hero worship of his dad and tunnel vision, but it really defangs the Iron Horde when they were an antagonist perfectly capable of carrying an expansion if they were handled as Blizzard initially intended.