This is an incredibly complicated question, so I'm glad the author put in the work to really try to flesh out the details. In the end I'd say the US's broken legislative system has forced the fed to make some really tough decisions. The decade following the great recession should have been a time of expansionary fiscal policy. Instead of congress investing in our future they argued and accomplished nothing. The board of the fed saw congress's failure and figured "if this country can't execute fiscal policy well at least we can step in with expansionary monetary policy". Came to kick them in the ass when covid rolled around, but it was also arguably responsible for one the best decades of economic growth in human history.