They had to raise the debt ceiling. They had to do this very routine operation. Previous to this... event, the debt ceiling had been raised ninety (90) times between 1941 and the present without any drama.
This time, the Tea Party-infused Republican Party decided to make it dramatic. This younger branch of Republicans that were just sent to Congress believed that they were sent with a mandate to basically take no prisonerd, to hold the line, to stay true to their "values," whatever those are.
With this latest roster of Republicans compromise (which had been the relative way of things decades past) was a dirty word this time around for Republicans.
But they must have known all along the debt ceiling would have to be raised. Not to raise ito would have meant the United States was defaulting on previous obligations. They would have had to "decide which bills to pay, and which bills not to pay," and all that.
Most important of all, from the perspective of the ruling class (this term 'ruling class' does not just mean the government proper), to default on the debt would have definitely spelled the beginning of the end of the American empire, and they certainly don't want that!