The Fed prints money through an auction/market involving only privileged actors (a small number of investment bankers). The new money then changes hands a couple of times before being distributed wide enough to have the desired macroeconomic effects. By the time it reaches you our me inflation has already set in. In those intervening steps, profits are made that dampen the effects of quantitative easing, requiring that the fed spend/create more money than it theoretically would need to in order to have the desired effect. That extra money can be thought of an "economic rent".
Silvio Gesell explores this concept in depth: https://www.community-exchange.org/docs/Gesell/en/neo/