Many forecasters, including FOMC participants, had been expecting inflation to cool in the second half of last year, as the economy started going back to normal after vaccines became widely available. 3 Expectations were that the supply-side damage would begin to heal.
Given their mandate, as long as there was something that could be done  to achieve the goals given to the central bank, however small the impact, then that something had to be done. Otherwise there was a serious risk of undermining the legitimacy of the central bank's independence.