This is a genuine question. There's probably an explanation for this I haven't thought of, but it just occurred to me and I thought I'd post it here. I'm sure a central reason would be that Japan was going to surrender, while Germany wasn't at the time.
Arial bombardment like that wasn't even an old fashioned way at that point. They went from taking pot shots at cities from one stupidly large cannon to having engineers invent a way to make a single flame cover an entire city between ww 1 and 2.