How did all this ‘evolve’?
Gravity tells almost the whole story, from the Big Bang to the present, when we have one monstrous black hole about to dine on another monstrous black hole.
In fact, this moment in the life of that larger black hole is beautifully illustrative of how it grew to such colossal proportions in the first place; i.e., by sucking in all the mass near it for billions of years, including other black holes, thereby growing ever larger — without limit, for all practical purposes.