Low interest rates definitely helped in the last few decades. Recently, yields have been rising though, which created some choppiness in the market. I think one of the main reasons the market hasn't responded in a big way yet is money supply: https://fred.stlouisfed.org/series/M1SL

The money being printed has got to go somewhere and a 1% return in the stock market (with high PE) is still worth more than a negative real rate accounting for inflation.