I think Bush personally selected Miers and shouted down all dissent. Maybe he told people that he'd "given them" "their" Roberts and now it was his turn. Maybe Cheney had something to do with it (see below). But I think this is Bush's show.
Since the 2000 elections conservatives and journalists have invented all kinds of rhetorical tricks to discuss and critique the Administration, basically because the President is obviously an idiot who isn't possessed of the wherewithal to make Presidental decisions. We all play along and say "Bush" did this or "Bush" did that when we all know that we're dealing with a strange oligarchy whose rules are invisible from the outside (and certainly have nothing to do with conventional American governance).
But I'll bet sometimes it really IS Bush. And I think this is one of those times. (More below)
What we all have to bear in mind is that Bush isn't just "guilty" of cronyism: he SINCERELY BELIEVES in it. It's the product of his strange, privileged life: he really believes that the loyalists who surround him are "the best people."
I mentioned Cheney. Cheney is smarter than Bush and sees what's in the wind: like Rasputin, he's starting to quietly prepare for the villagers with torches who would come out of the woodwork once 1) he was no longer King of America and 2) people find out everything he did. Cheney called Rush Limbaugh to "reassure" him about Miers. What does this mean? Cheney has no scruples at all; he won't mind screwing the court for decades in order to get his "get out of jail free" card.
But I still think it's Bush. He's still inflated with his "mission accomplished" megalomania. Remember that when Bush says things are "improving" in Iraq he GENUINELY BELIEVES IT. He is a strange, stubborn, proud, stupid man.