From the article : It might want to keep some fiscal space in reserve in case of another disaster.
My comment: It's too late for that. Yellen says go big now. What happens when the next financial crisis hits (ie the bubbles burst) ? Go even bigger then ? It's a debt spiral from which there is no escape. At some point rates will rise due to the extraordinary amount of fiscal debt which I think will be at least $40Trillion by 2026. We're already over $30Trillion with the $0.9Trillion rescue package passed in December and the proposed $1.9Trillion that Biden wants. $2Trillion plus annual deficits for as far as the eye can see.