The best analysis of why President Truman decided to abandon the plan to launch an amphibious invasion of Japan in 1945 is:
Truman realized that the invasion would cost too much money and American lives.
This statement reflects the primary concern for Truman and military planners regarding the potential high casualties of a full-scale invasion of Japan, as well as the substantial costs involved. The alternative of using atomic bombs, which was seen as a way to bring about a quicker end to the war with fewer American lives lost, played a significant role in his decision-making process.