Washington knew the BOMB worked. Why not wait to see the results before spending lives on the Okinawa invasion? Okinawa was needed as a base for the invasion of mainland Japan. But what was the big hurry if the BOMB could end it all?
It is still another piece of land under our control. I would assume the U.S. wanted to get all the land they could so when the war ended, it could be easier to deal with.
Also on the plan A and ‘long shot’, we only had 2 bombs, what were we to do if the Japanese had not surrendered like most of the Generals had wanted to. We still would’ve had to invade IMO.