I will very likely need CNN's Elizabeth Landau to sketch this out for you better than I can, but here goes. The perception of a black hole is that it just sucks in everything it gets its hands on. According to a study recently published by Science, not so much. It's true that if you go past the event horizon, that's the ballgame. But getting sucked into the gravity well, not necessarily, and that 'not necessarily' may have played a part in how the Milky Way got formed.
As I'm reading this, Landau asks you to think of a sink drain. You pour cold water down the drain, it's going to, well, go down the drain. The same is true here; cold gas goes through the event horizon. But now try and pour steam down the drain. A little bit, the odd droplet, might find its way in somehow, but really just about all of it is not going. That also happens here; according to the research, led by Daniel Wang at Massachusetts-Amherst, in order for matter to get sucked in by a black hole, it must lose both heat and angular momentum. In order for the black hole to eat, it generally has to spit 99% of the matter back out. That's the heated matter, and it, well, creates heat in the area around the black hole. The bigger the black hole, the more matter is processed, and the more matter is processed, the more is rejected, and the more matter is rejected... the bigger the resulting galaxy.
So basically, we are as watermelon seeds. If watermelon seeds were hot. And the universe was wet and sold by the pound and regularly smashed by washed-up comedians. This analogy got away from me in a hurry.