Another factor to consider is the thermal massing of the structures. A lightweight steel structure is much easier to air condition in the swampy Florida climate than a heavy-duty concrete bunker. Given France's cooler climate, there's not as much worry about the structure soaking up the heat from the summer sun and retaining it for days or weeks on end.
It's the same reason why tropical architecture has historically been mostly wood, while stone structures tend to be found primarily in cooler areas. Before everything had central air conditioning, structures were designed with the local climate in mind; warming a building up wasn't difficult (build a fire) so keeping them cool was the primary concern.
