As far back as late 2017, there were just 3,671 domestic listings, according to the Wall Street Journal. The number had declined due to the growth of venture capital and private equity.

"The number of public companies in the U.S. has been on a steady decline since peaking in the late 1990s. In 1996 there were 7,322 domestic companies listed on U.S. stock exchanges. Today there are only 3,671. Easy access to venture, growth and private-equity capital means that companies no longer need to pursue an initial public offering to fund growth or access liquidity," the WSJ wrote about 3 years ago.

Since then, the number has continued to decline. Yesterday on CNBC, it was reported that there are now less than 3,000 public listings. But there's now more than 7,000 ETFs globally.