A Bush rule enabled businesses to automatically enroll  workers into 401(k)  plans. If the workers failed to specify how they wanted their money invested, the company was required by law to place their retirement money in investment funds that, for the most part, relied heavily on stocks. About two-thirds of workers opted into such plans before 2006, and participation was expected to rise to more than 90 percent with an auto-enrollment provision.
The administration specifically rejected safer investment options when Congress left it up to the Bush administration to determine what categories of funds should be allowed. The administration rejected the pleas of stable value fund managers to have their product be available as a stand-alone option for automatically enrolled workers, reasoning that the funds would be vastly outperformed by stock-heavy investments over the long term. The administration asserted that the stable value funds would not provide "meaningful retirement savings over the long term."

From:
http://www.boston.com/news/nation/washington/articles/2009/04/05/workers_steered_to_high_risk_investing/