Fair question, but there's a pretty direct line. ZIRP means that huge capital managers (sovereign wealth funds, pension funds, 401k managers, etc.) get very, v

Fair question, but there's a pretty direct line. ZIRP means that huge capital managers (sovereign wealth funds, pension funds, 401k managers, etc.) get very, very little money on the super-safe stuff they like to buy. They need to make returns somehow, so if a VC is promising them 15% returns, that sounds quite promising compared to T-Bonds that return 1.5%! But over the last two years, the yield on super-safe investments now looks more like 6, 7, 8, 9%. That makes a high-risk investment like VC much less attractive, by comparison. If VC is less attractive, less capital flows to their funds; smaller VC funds means much more discerning, stingy startup investment.