Basically they can only control inflation in the future, and they believe the inflation we've just seen is a result of the one-off of the pandemic response. Given that the interest rate mechanism affects inflation by increasing unemployment and harming the economy, they don't want to do that until it's necessary.

(I should note that it's theoretically possible to do inflation control by fiscal policy, i.e. mop up some of the spare money by taxation, but that's obviously not going to happen)