It depends on the country. If you live in a place that - traditionally - had only an expected few days of really hot temperatures every summer, it wasn't worth the investment. With climate change, the temperatures are now higher and the heat stretches longer.

Agreed, the EU is not that small and Southern countries had to go before northern but now I feel it is pretty normal. Might be my circle of course. Or in a shorter way; YMMV. I know zero people without aircon and one couple live fulltime in a yurt.