> If you know that the US doesn't have enough refined uranium for another uranium bomb […]
There was no way for the Japanese to know what the US was capable of. It was wishful thinking with zero evidence on the part of the Japanese leadership.
So did the Germans, but it's not because the biggest industrial power on earth (in both demography and industrial output), with its capacities fully intact because the war never took place there, that smaller countries diminished after years of blockade and critical infrastructure bombing can do it too…
If the Japanese projected their own capacity on the US, they were ripe for a bad surprise.
There was no way for the Japanese to know what the US was capable of. It was wishful thinking with zero evidence on the part of the Japanese leadership.