Also when you are like me and only care about the campaign:

“You fool, why the fuck would you want to switch to the campaign? Good luck in finding out where we hid that button in this overly convoluted UI. Oh yes, and because you are not planning on forking over additional money to us, we’ll restart the game in stingy campaign mode. And no, you cannot be smart and just start the single player executable directly, because we made sure it won’t run when not launched through the game we actually want you to play.”