There is always a battle for inflows of money between bond and stock investments. Is money looking for the saver heaven in bonds or is it worth the risk to buy stocks? At any given point in the economic and stock market cycles that battle exists.
Today though stocks are relatively expensive when comparing historical P/E ratios the return on bonds have fallen sharply thus making the risk of buying stocks more attractive. If you can only earn less than 2% on a 10-year U.S. government bond, the investor must consider buying a stock like AT&T which pays a 6% dividend. Yes, stocks are much less safe but how risky is AT&T and over 10 years which will make more money as an investment? That is the decision.
As bond yields fall stocks look better as an investment despite the volatility. Overseas, where bond yields on government bonds are much lower and in some cases negative then in the U.S., money flows to the U.S. and that money finds a home in our bond and stock market.