Where else can you put your money? Interest rates on bonds are non existent and the govt. is spending money like water. Plenty of dollars looking to be spent and businesses benefit in the short term.
Rational irrationality comes to mind.
Take a look at International equities - especially Emerging Markets like Asia. The P/E ratios of International stocks are in many cases much more reasonable than US. US "Value" stocks are also another potential option for the same reason. Lastly, look to inflation hedges. TIPS are awful at the moment because of negative yields, but there are funds out there that can buy a combo of foreign currency, gold, real estate, commodities and TIPS (when those make sense again) that might be an option. Also VERY short term (1-2 year max) bond funds..you really don't want to be holding bond funds with longer maturities in a rising rate environment (bond prices fall when interest rates increase).