GDP growth usually requires investment in business enterprise. But, investments may have returns either in the short-term or in the long-term. Investment which responds to consumer demand yields immediate benefits, and is often favored.
Investments vary in quality: for example, a rich government investment firm can increase GDP by just building cities which will never be occupied in the desert.
Consumer demand and public debt
Individuals borrow money, and they have to repay them. The purchasing power of people correspondingly decreases.
High public debt
When the money they collectively borrow is close to the (projected) GDP (national money production), there is trouble - it means that people are collectively incapable of repaying their debts.
This has happened in USA in 1929 and in 2009; thus Americans have financed their high individual standard of living with borrowed money they cannot repay. This eventually may lead to most individuals in USA being less worthy of credit and investment - leading to economic depression.
Global savings
Increased prosperity in many parts of the world has resulted in greater amount of money becoming available for investment. IMF tracks this number - it exceeds the world’s GDP 5-fold, at 83 trillion $ in 2009.
Investment managers seek to utilize this money by investing in something which yields good return and low risk, with emphasis being on one or the other depending on their recent experience (and partially based on their long-term education). Their willingness to take reasonable risk is important to spur continued GDP growth.