It's the closest to printing money as the real world gets. "Hey here's an insane amount of money at 0% interest rate so you could literally invest in ANYTHING and make free money. Go ham."
Lets remember what causes slowdowns in productivity, panics, the great depression, the recession etc: people being slammed with too high interest rates for what's feasible for them to repay when times are tough. If the fed offered low interest rates directly it would be a different world. Remember also, the world is an auction house, so when people get these kinds of perks and you don't, your money doesnt go as far.