In my experience most homes/apartments in Europe are stone/cement/brick and many were built before central heating/cooling was a thing. US homes being much new

In my experience most homes/apartments in Europe are stone/cement/brick and many were built before central heating/cooling was a thing. US homes being much newer, and built from wood, means getting air ducts in isn’t such a huge deal. So European homes often heat ultimately via hot water pipes (radiators, heated floors), etc but there isn’t a way to cool using the same mechanisms. Of course this is a huge generalization.