Because it never has made an full recovering. 2016 fed only started on making lower balance sheet but never making much progress: https://www.federalreserve.gov/monetarypolicy/bst_recenttren...
Interest rate are similar: https://fred.stlouisfed.org/series/FEDFUNDS
Europe even worse than these above. We leave us without tools for economic troubles when we are declining to raise interest rate and sell assets on business cycle peak.