Actually, the answer is quite simple – and, at its core, it is not a matter of political posturing or point-winning, however often it devolves into that. The cause is Congress's continued unwillingness to deal with Medicare, Social Security, and the Pentagon.
The fact is, despite all the hubbub of the past two years, the federal government has still not made any meaningful spending cuts. And that is mostly because meaningful spending cuts are virtually impossible without addressing entitlements or the Department of Defense.
Congress and the president tried to do just that in the 2011 debt-ceiling deal, yet the fiscal cliff deal shows that Washington, when faced with such cuts, apparently doesn't have the stomach to let them take effect.
So Republicans sent to Washington specifically to rein in government spending have next to nothing to show for it. And the mounting fear is that they might never have anything to show for it – that the classic Washington inertia to do nothing is slowly consuming the energy of the 2010 tea party revolution.
Senator McConnell added Sunday: "Now it's time to pivot to the single biggest threat to our country, both in the short term and the long term ... and that's reducing spending."
Indeed, some Republicans are growing increasingly desperate. They believe that Congress will never get serious about bringing its spending into line unless it is in crisis. So better to manufacture one now, and solve the problem, they say, than to let things linger and eventually become Greece.
At the same time, Washington knows that responsible, long-term fiscal planning cannot move forward until spending is brought under control – it's just that the prospect of entitlement reform or Pentagon cuts are so politically unsavory that the day of reckoning is postponed again and again.