Board Thread:Questions and Answers/@comment-8864605-20140928173400/@comment-14267015-20140928180644

Kraang Subprime stated that the Kraang didn't want to invade without taking care of the Turtles. Likely because the Kraang consider them the biggest threat to them and the Turtles did manage to take down a Technodrome. Basically, the Kraang weren't going to start a major invasion without doing something about the heroes in a half shell. If they killed them, great. But they had Kraang Subprime become Irma, it's unknown if there was an original Irma that they kidnapped or if the Kraang made her up, and befriend April so there would be a chance of him also encountering the Turtles. Eventually this would have led him to their lair which the Kraang could then portal to and destroy. As we've seen, the Turtles are now on the run and have almost no resources, greatly reducing their threat to the Kraang's plans.