Today's Republican party is defined by deep hostility to anything that gets in the way of upper-bracket tax cuts. That includes debt reduction.
Trouble is, debt reduction is too popular to oppose outright.
Gee, we'd love to reduce the debt, but, sadly, it can't be done. So the only option for the surplus is, alas, to cut taxes. Indeed, it has become a Republican truism that if you keep the money in Washington, it's as good as gone. And Bush is absolutely right when he says we can't pay down the debt because politicians in Washington want to spend it. He just neglects to mention that the politician in Washington most responsible for this state of affairs is Bush himself.