Because it was never really intended to work:
The best explanation I’ve found for why the stimulus didn’t work is this graph from the GAO analysis of the stimulus act. It shows pretty clearly that the 76 percent of stimulus spending through the first four months went to fill in the gaping holes in Medicaid and state budgets. In other words, the stimulus isn’t acting like a pole vault lifting job creation above the baseline. It’s been acting like a crutch to keep state budgets and payrolls from imploding tumbling.
And I warned you liberals of this – if you send money to a State, it won’t go where you want it to go, but where that State figures it needs it. Money, as they say, is fungible…you can send a billion to NY for highway improvements, but NY might very well plug their budget hole with it. And what will you do about it? Demand the money back? Its already spent. Given that the States in the worst shape are largely liberal-governed States, its almost a certainty that any money actually used for stimulus is just pure happenstance…after looting spendulus for their own purposes, there just happened to be a little left over (or, more likely, a construction firm or union which needed to be paid off).
It won’t work: the only way to get some government money to stimulate the economy is to provide grants to people who are willing to invest their own sweat equity in opening up mines, sowing fields or starting up factories. You give that money to government, and it will be wasted. You give it to large, failed firms and it will be wasted. You give it to people who are willing to work for a living, and it will be used…and they won’t need a trillion dollars.