why did united states drop the atomic bomb. when it killed some of the soldiers?

This question must refer to the Americans who were held as prisoners of war in Hiroshima on the day the first atomic bomb destroyed that city. Many were members of the crew of a bomber known as the Lonesome Lady that was shot down over Hiroshima a couple of weeks beforehand, and they were among the thousands killed by the blast. Many Americans and British POWs were held in and around Hiroshima, and most, including some of the crew of the Lonesome Lady, survived the explosion. As for why President Truman decided to drop the bomb in view of these facts, there is no evidence that he was specifically aware of the presence of these prisoners (though he must have known that Allied POWs were held in most Japanese cities). In fact, Truman used the brutal treatment of American prisoners at the hands of the Japanese military as a justification for using the bomb. In a radio address shortly after the Nagasaki explosion, he told the American people:

Having found the bomb we have used it. We have used it against those who attacked us without warning at Pearl Harbor, against those who have starved and beaten and executed American prisoners of war...
https://teachinghistory.org/history-content/ask-a-historian/22693

https://www.historynet.com/imprisoned-ground-zero-american-pows-hiroshima.htm

https://www.pbs.org/newshour/show/how-a-hiroshima-survivor-helped-remember-12-u-s-pows-killed-by-bomb