President Obama's 2009 fiscal stimulus package, estimated to be $805 billion by some, is roughly 6 percent of the annual U.S. gross domestic product (GDP). Six percent, incidentally, is about double the historic average U.S. annual economic growth rate.

The question that begs to be asked is why, despite this gigantic stimulus, the U.S. economy is still growing at a subpar rate.

Indeed, there are two more reasons that the economy should have rebounded a lot faster.

One, economies usually post high growth rates coming out of deep recessions. A related fact is that much of the growth so far came from inventories adjustment, so the real expansion is even slower.

There are many explanation for the weakness, but Gary Shilling, president of A. Gary Shilling & Co, offers one useful figure.

He said of the $805 billion amount, 46 percent of it was saved. Another way of looking at it is that only 54 percent, or $435 billion, was consumed or invested.

People are on a savings spree for the first time in 25 years, said Shilling on Bloomberg TV.

He cited four reasons that certain people may want to save.

One, those born after WWII haven't really saved for their retirement yet. Two, people are concerned about losing their jobs. Three, many have already exhausted the value of their homes through home equity loans. Four, the public doesn't expect the stock market to rise like it did the 80s or 90s, so asset appreciation won't save their day.

You got a lot of reasons people want to save….[When] the government hands them a big wad of dough, they save about half of it, said Shiller.

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