Egregoros

@sun From what I know living in a very temperate area of the country, it's mostly because it was basically a luxury until the last twenty years or so, and minds change slower than the heat raise. For common people it boils down to that, way too expensive for something you use at most two weeks a year, and fans did the job.

Extrapolating (words words words):

Heatwaves of this magnitude are a new thing and until now we were mostly concerned about keeping heat in the winter by insulating the houses.

Proper AC units were already more common in the southern parts of the country where heat was always an issue, but for most people (who rent) it will be either suffocate indoor or save up to buy a proper mobile [suit Gundam] AC unit, because I don't expect any sudden move from the landlords to upgrade their properties to face the raising temperature unless government legally force them to.

Speaking of gov', there's also legal reasons specific to France impeding on AC adoption but I didn't read about that at all, just food for thought.

Another thing is that the general Internet discourse about this issue completely ignores that Europe is not a single country with a single climate. Europe is not just Germany or France, same as the USA are not just southern California or Texas but dozens states spanning an entire continent. I'm pretty sure the willingness to use air conditioning and the means and readiness to face extreme temperature will greatly change between say a fella from Fingolia and another one from Greece