Why not?

The Fed first expanded its balance sheet in the wake of the 2008 financial crisis. Through three rounds of quantitative easing (QE), the Fed expanded its balance sheet from under $1 trillion to $4.5 trillion. When the central bank started QE, then-Fed Chair Ben Bernanke swore the central bank wasn't monetizing federal government debt. He said the balance sheet expansion was an emergency measure and that the Fed would eventually sell the bonds it was buying.

The Fed didn't get around to balance sheet reduction until 2018, and it did so at a relatively slow pace. By the time it ended tightening in August 2019, the balance sheet was just below $3.8 trillion. In all, the Fed shed about $700 billion from its balance sheet in a little more than 18 months.