But it isn't really investment. You want long term growth, the private sector has to feel ready to jump in. The large national debt, whether relevant or not is on peoples minds including the private sector. If there isn't at the very least an attempt to get that **** in line, businesses will hold back capital.
Edit:
FFS you've had the last three years of QE 1, 2 and 3 that was supposed to be "short term stimulus" that hasn't really had any actual growth impact on the economy (given that GDP is not increasing).