I should probably be offering some more coherent thoughts on Miers than "conservatives dislike her", although watching their heads go "pop!" sure is fun. Poor kids. They thought electing a cipher and surrounding him with conservative ideologues and Republican wisemen would result in a sort of Robo-Republican, a candidate genial enough to take office and suggestible enough to govern -- pun not intended -- right. Instead, Bush reacted as most small men in big boots do and surrounded himself with folks even less qualified than he. With his Spidey Sense tingling, Bush staffed his administration with a who's who of neocons grateful to come in from the cold and Texan loyalists eager to erase their regional insecurity through national actions. Classic spokes-and-wheel formation -- the connections and loyalty all flowed towards Bush, not the party or each other.
What was different about this case was that all manner of conservatives got shafted. From the theocrats to the libertarians to, eventually, the neocons, the only group who found Bush a reliable genie were the plutocrats, and they're more self-interested Rockefeller types than ideologues. But that's because Bush was never into ideology, he was into power, into winning. That's what happens when you pick a cipher. In politics, if you're not driven by ideology, you're driven by drive. And with that sort of self-referential motivation schematic undergirding the candidate, better bet he's no more wedded to your agenda than his.
Of course, the spurned factions of America's conservative fraction turned to that old standby to explain the defeat: fantasy. Bush was like them "deep down", he just need to win reelection, boost his poll numbers, pass CAFTA, fill the first Supreme Court seat, blah blah blah. What's hitting now is the realization that Bush is really as small and short-sighted as he seemed, it wasn't some plan or bit of overly-complicated "strategery". This time, there was nothing holding him back and, indeed, much pushing him forward. Roberts won with room to lounge, Bush needed to reinforce his base, Republicans needed to change the agenda...if there'd ever been a moment for a pitched ideological battle over a wingnut nominee, now was it.
But in the end, Bush really was a provincial, uninterested power-amasser. He wanted a Texas crony and, since conservatives deep-sixed Gonzales, Miers was the logical fallback. There's no political upside to the pick but then, for the reelected Bush, there's really no downside either. Where the fuck are congressional Republicans gonna go? What's the Christian Right gonna do? Get behind a neanderthal like Roy Moore so the country can elect a liberal like Hillary Clinton? Let 'em try. Bush has 'em by the balls. The Christian Right's influence comes from control over the Republican party, but since Bush shows little evidence of caring about the long-term health of his party, they've got nothing on him. Nobody does. He can pick who he wants.
And so he did.