That's only because we're in drought conditions. IN a normal summer we regualrly get 70F+ dewpoints. But it doesn't sustain year round like in FLorida. Yesterday the dewpoint was around 40F but it reached 98F. IT made it over 100F ambient at least 6 ro 7 days this summer. I'm in SE Iowa, my design consditions for temperature and humidty are nearly the same as for most of Florida. It just doesn't stay hot here, but we also have something called winter. The dewpoint thsi weekend is expected to jump up to 70F this weekend and some possible thunderstorm (finally!) come through.
I don't open windows in my home very often because of dust, noise and it's a PITA. I have 39 operable windows with storm windows, so even opening 1/4 of them takes a little time since I have to open 2 sashes on each one. W'ere not hoem to close them at the ideal time of around 10-11AM either. I just assume leave them closed and pay an extra $10-20 on my electric bill.
Besides, if you look closer, the dewpoint raises overnight as the ground and plants cool off. It will get up to 70% RH or a dewpoint around 58F, which is much higher than it is inside my house. It's around 47-51F dewpoint.
Don't underestimate the climate in the central midwest. It's much hotter and more humid than most eople give it credit for... but it only lasts for 3-4 months, then it turns wicked cold and that white flaky stuff falls from the sky.