No mention of demographics, the inflation rate, the T-bill risk-free rate of return, or of the GDP growth rate (I'm not saying any or all of these ARE correlate

No mention of demographics, the inflation rate, the T-bill risk-free rate of return, or of the GDP growth rate (I'm not saying any or all of these ARE correlated, they're just things I think it would be obvious to analyze before just declaring it a mystery)? Well, I guess he does mention some of them are correlated with the stock prices, but then ends with "nobody knows anything".