It’s a complex event. Those were the high level options, which remove the political factors.
In the context of being in the middle of bombing campaigns of cities, the moral turpitude of mass killing of people was long pushed aside. Total war meant everyone was part of the war effort.
So you’re left with a couple of factors. The prospect of invasion, the likelihood of getting a peaceful settlement, and the prospect of Soviet involvement.
Bombing and starvation wasn’t working fast enough to cause the intransigent military junta to bend. I think the idea was that the shock of atomic bombing would empower the collapse of the government, and cow the Soviets.
At the end, they came to the table, and the US accepted a conditional surrender.
Personally, I think if folks are going to be intellectually honest about the atomic bombings, you have to have the same position and advocacy for scaled destruction of cities in general. The firestorms, created by napalm and phosphorus and inflicted on Tokyo, Dresden and Hamburg among others were no less a horror. Decrying the tool allows people to explain away from the context. A more efficient killing machine doesn’t make the killing any more or less righteous. I think the Japanese perspective of this has been around embracing the pursuit of peace. A worthy goal that we’ve abandoned.