The bull market was nothing to do with historic valuation comparisons so dear to those who, in essence, say that market's continuous advance was immoral.
Money flows from buyers to sellers.
If the sellers vend newly printed shares and used the cash for anything other than buying other shares, that reduces liquidity. Historically, float change is the best leading indicator of future market direction. We track the change in the float, that is, the number of shares outstanding. Then we keep track of the dollars moving in and out of the checking accounts of stock-market participants. We can only track a portion of the float and changes in it on a timely basis.