Yellen argues that it’s because investors are expecting some kind of government action that will stimulate growth. The only problem? She’s lying.
What’s really behind the market growth? The fact that world governments are investing in the market because it’s the only way to get returns. The US government does it because the bond market is flat. The Japanese Government is doing it because they need to pump up their rapidly inflating currency.
Banks around the world, as well as governments (and in some countries, the official banks of their respective countries) are taking the valueless over-inflated currency and stashing it in the market in order to get a return, and they’re even looking to do more.
So no, Janet Yellen, the market isn’t expanding because of policy. It’s expanding because of policy failures and desperation. It’s a bubble whose pop is going to make 2008 / 2009 look like dropping a twenty out of your pocket while walking to work.