They are pricing in what the potential of the free money is and not what it actually is. That is your "math".
Since the economy is too broken for anybody or any entity to actually have the kind of trillions of $ laying around to be relentlessly buying stocks, that only means central banker free money must be at the root of the buying.
There has never been an economic recovery in U.S. history with short-term cash rates remaining near zero percent for this duration of time. The 1932 to 1937 period does not count because unemployment remained stubbornly high during that period and the DJIA did not return to its all-time high of September-1929 until 1954.