The idea that the stock market has been shrinking in any meaningful sense is kind of silly. Market cap means something, but the number of shares in a company by itself is meaningless.
If that's the article's metric, surely they note that corporations have executed literally trillions of dollars of stock buybacks over the past few years, right?
Record new issues is one of the classic signs of a bubble [...] The new big three IPOs will dwarf the entire amount raised during the [1999-2000] tech bubble even when accounting for inflation.