Because interest rates will never go back up, or if they do, they will be counterbalanced by inflation. This is the view of Ray Dalio at Bridgewater and (presumably) many other very smart people. I'm not that smart, but I agree.
Thus, cash and cash obligations are no longer stores of wealth. Equities are, unfortunately. High volatility is just the price you pay. Equity prices are honestly not that high if this scenario plays out.