Its because shareholders are largely content with short term gains. They do not care about the long-term interests of the company because they are not long-term investors. Forget about the fact that they only care about maximizing profit.
Moreover, shareholders just seem to be stupid.
The best form of regulation for all these sub-prime loans would have been if shareholders of the big banks had fled the banks after seeing these kinds of assets on the books. But they didn't. They bought everything hook-line-and-sinker. They took all that loss in value. They continued to support, through not selling their shares, huge salaries and bonuses to corporate managers.
And they continue to do it today. They continue to invest in junk, pump-and-dump companies. They are lured in by false promises and never seem to learn.
Plan for eliminating the national debt in 10-20 years:
Specific cuts; defense spending: http://rolexian.wordpress.com/2011/01/03/more-detailed-look-a