They don't care about deficits
Once again, Krugman:
the GOP is not now, and never has been (at least not since the 1970s) concerned about the deficit. All the fiscal posturing of the last couple of years has been about using the deficit as a club to smash the welfare state, with the secondary goal of frustrating any efforts on the part of the Obama administration to help the struggling economy.
The entire debate has been fake. If you don’t understand that, or can’t bring yourself to admit it, you’re missing the whole story.