I haven't fact-checked anything about this, but this bomb (and its friends) were probably dropped here because it was an active military airport during WW2 and

I haven't fact-checked anything about this, but this bomb (and its friends) were probably dropped here because it was an active military airport during WW2 and the US was desperate to put a dent in Japan's air power. After the war, thorough ordinance disposal was very likely a secondary consideration rebuilding the country. (And its runways.)