Considering that the US dropped written warnings explaining that the cities were about to be bombed, you'd think the Japanese would do more to evacuate. Why didn't this happen?
They weren't warned before the bombs dropped. Leaflets concerning the atomic bombs were dropped after August 6 when Hiroshima was bombed. Nagasaki received pamphlets regarding the Hiroshima bombing after it was bombed. There were never any plans to warn the Japanese about the upcoming atomic attacks. This would've endangered the bomber crews as well as the bombs themselves which were irreplaceable. Check out this blog by Alex Wellerstein regarding the confusion about warning leaflets http://blog.nuclearsecrecy.com/2013/04/26/a-day-too-late/
In addition to what u/Jobambo said elsewhere, Alex Wellerstein is also known as u/restricteddata, and has posted here on the subject as well:
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