> In southern Europe this is false for many weeks during the summer.

This is also now often false in non-southern Europe as well.

Apparently one of the reasons why French don't have air conditioning is because nights tended to be cool in the past, and so people left windows and doors open while sleeping creating drafts and letting the masonry cool.

But in the last ~15 years nights have been as hot as days at times, and so this strategy is no longer effective: you're cooked at night as much as you're cooked during the day during the heat domes. So the all-the-AC-all-the-time thinking of the US may be excessive, nowadays so is the never-AC thinking of many people.

You don't need to get down to 22C, but least <27C will save the lives of many people, especially the elderly (unless France wants to save on pensions?).