I have to imagine the heat/humidity is just as bad in places like LA/Atlanta that have previously hosted the summer olympics. Did they just not care about heatstroke back then?
There was a Doha marathon ran this year at midnight, still running at around 30°C and needing crazy heat counter measures to be runnable.
It was their test drive to see if the same setup would work for Tokyo, but it appeared the Doha marathon was still a hell to run so they gave up and moved the location to somewhere cooler.