Have you been to Paris? Go on google earth and poke around. Theres no place to put the condenser. Most people rent so even if there was they can’t drill holes for the lines and even if they could, most buildings are historic so they can’t. Central AC/heatpumps on some rooftops could work.

Window units can be added to basically any existing home. And like you said roofs are an option. France could afford AC with their relatively cheap power but it’s just culturally and politically unpopular despite heat related deaths being extremely high and loss productivity it’s certainly more than the cost to retrofit.