Maybe he just doesn't want any of his plan's actually scored by an objective party like the Congressional Budget Office (CBO)? Check out what the CBO said about Obama's last officially released plan, released just a matter of months ago:
- If the President’s proposals were enacted, the federal government would record deficits of $1.4 trillion in 2011 and $1.2 trillion in 2012. Those deficits would amount to 9.5 percent and 7.4 percent of gross domestic product (GDP), respectively. (By comparison, the deficit in 2010 totaled 8.9 percent of GDP.) Those deficits would exceed the ones projected to occur under current law, by $26 billion and $83 billion, respectively.
- The deficit under the President’s proposals would fall to 4.1 percent of GDP by 2015 but would generally rise thereafter. Compared with CBO’s current-law baseline projections, deficits under the proposals would be about 0.5 percentage points of GDP higher in 2012, 1.3 percentage points higher in 2013, and 1 to 2 percentage points higher thereafter. By 2021, the deficit would reach 4.9 percent of GDP, compared with 3.1 percent under CBO’s baseline projections. Over the 2012–2021 period, deficits under the President’s budget would total $9.5 trillion, compared with $6.7 trillion under those baseline projections.
So his last budget, released about 5 months ago actually increased deficits and spend more money than was expected at the time. If coming up with something grand was so important to him, why didn't he do it then? It's not like our budget situation was vastly different back then. And back to the original point, my guess is that what he was offering to the GOP (and to the American people) probably had a lot less cuts than some of the headline figures would lead you to believe and that is why he doesn't want to provide any real details to anyone.