If we model real interest rates as the "price" of saving, then we can examine changes in the demand for saving and the supply of saving to see whether we can account for the shift. The demand for saving is determined by everyone who wants to borrow now (to invest), and the supply of saving is determined by everyone who wants to save now (to consume later).
The supply of savings has increased "due to demographic forces, higher inequality and to a lesser extent the glut of precautionary saving by emerging markets." On the demand side, "desired levels of investment have fallen as a result of the falling relative price of capital, lower public investment, and due to an increase in the spread between risk-free and actual interest rates."
In other words more people want to save (increase in supply) but fewer investors want to invest (decrease in demand). Both result in a lower "price" of saving.
Because the return to saving is lower, savers should expect to earn less. This has enormous implications for the defined-benefit pension plans that characterize government pensions. In particular, these pension assume that they will earn 7-8% (nominal), and make payouts based on this assumption. If pension funds earn less, then there will not be enough money to go around when the pensioners eventually retire.