I think it was that Rick separated the realities where he was the smartest guy in the universe from the ones he wasn't, and made those inaccessible, thus they were not really able to travel into infinite realities, they were just realities where he was the smartest guy, and Evil Morty was tired of not being able to escape Ricks.
Rick is a big fish in a pretty big bowl, Evil Morty broke the bowl into the ocean.
At least that's what I understood, I could be wrong.