Central banks: Why stop short of equities?

The Federal Reserve and the ECB are buying practically all non-bank debt: government bonds, Investment Grade and High Yield corporate bonds, commercial paper, loans to SMEs. But neither central bank is buying equities . W hy stop short of equities? The equity wealth effect is significant, especially in the United States: it could be useful to lift share prices in a crisis, but central banks refuse to do so, even in a simple form such as purchases of equity ETFs; A first explanation is the presence of moral hazard: central banks do not want to insure equity investors against risk; A second explanation is that the equity market is not being used to finance companies, especially in the United States given the share buybacks; Risk for the central bank is not a convincing explanation, since the central bank would be buying when share prices are clearly abnormally low.