Could be lot of reason.
Older European cities with high-density stone buildings and less green space often trap heat more effectively than typical U.S. suburban layouts.
Europe has a larger proportion of elderly residents (aged 80+), who are the most susceptible to heat stress.
You just picked a data and are trying to fit your narrative on top of it without really considering all possible aspects.
Could be lot of reason. Older European cities with high-density stone buildings and less green space often trap heat more effectively than typical U.S. suburban layouts. Europe has a larger proportion of elderly residents (aged 80+), who are the most susceptible to heat stress. You just picked a data and are trying to fit your narrative on top of it without really considering all possible aspects.