Bruce Bartlett largely blames low inflation and low interest rates:

According to the Federal Reserve Bank of Cleveland, none of the preconditions that historically are necessary for a significant budget deal are now present. Inflationary expectations continue to fall and real interest rates are very low. Hence, it is impossible for politicians to promise any benefit from large spending cuts or tax increases that would materially improve peoples’ lives. The benefits are purely abstract.

Daniel Gross adds:

Deficit scolds have always said that the U.S. could become the next Greece if it fails to close its deficits. But in the last several years, as deficits have exploded, America’s borrowing costs have plummeted. Meanwhile, in contrast to Greece, the U.S. private sector has thrived in recent years. Profits have soared to historic levels, and the stock market has doubled since March 2009. Looking solely at the charts of the stock and bond markets over the last few years, you’d never guess America has a woeful fiscal situation.