That’s true, though at the time you really do have to remember that the United States (with assistance from Canada, the UK, and Mexico), was truly the only allied nation (and probably any nation at all) at the time which could successfully pool together the resources, manpower, and scientific genius to accomplish the feat of unlocking nuclear fission and nuclear weapons.

Britain was under constant air attack, threatened with invasion, and most of its manpower was drawn to the war effort, and the Soviet Union was all hands on deck for the war effort with the vast majority of the country devastated.

Plus allied physicists can no idea how far along the German or Japanese programs were or what they would do if they reached the bomb first.

Those physicists by extension had no idea how or when their efforts would be used. They simply did their job and accomplished one of the largest breakthroughs in human technology. I doubt very many expected that their efforts would be thrown at Hiroshima and Nagasaki, especially since they anticipated using the bombs on Germany and Japan wasn’t even a second thought.