You need to know that to publish game you need thing called money.How do you even function?
Ok, accessing simplistic mode:
Ok, let's say Disney saw what Ninja Theory was capable of and called them up. Ninja Theory gave them a sample of what they could. Disney asks Ninja Theory how much it'd cost to make it happen. Ninja Theory gave their numbers and Disney agreed.
They are publishing Hellblade because they favor that game over the others. You do know Hellblade is theirs ALL AROUND right?
http://dictionary.reference.com/browse/money
To publish game you need big money.
http://www.ign.com/articles/2006/05/06/the-economics-of-game-publishing
If they refused Disney and other publisher, they didn't had money to publish Hellblade or any other game except for indie stuff.
Hopefully it enlightens you a little on why people work for publishers http://itlaw.wikia.com/wiki/Videogame_publisher