Shutters and closing them. And that includes the big shutters over the French doors between the terrace (or deck — why does the word "terrace" sound too fancy to me?) and the living room.
Does anybody in America have shutters like these? We don't close them in the summer, because it stays light until bedtime anyway. But in winter, it gets dark early and the shutters give you privacy as well as a little extra insulation from the cold and wind.
With shutters like these, you don't need heavy drapes over the windows. Or blinds. In San Francisco, that's what we had: either ugly drapes, or mini-blinds, or vertical blinds. I think shutters make a lot more sense.
When you go away and leave the house empty for a few days, the shutters are also a security feature. They make it that much harder for burglers to get in.
The only reason I can think of to explain the shutters on all the windows in France is the country's history of warfare — which goes back to pre-historic times, actually. In America, we don't have that.