It's not necessarily that smoking is a larger percentage of the population. It varies, but stats show a similar percentage more or less... it is a bit higher in Europe on average than in the US on average — but both places are large with varied amounts of smokers. It's more that people are outside near each other more in Europe.

https://worldpopulationreview.com/country-rankings/smoking-rates-by-country

In Europe they're walking down the street, sitting outdoors at cafes, hanging out in the city center, etc. Whereas in the US, people are often driving from place to place to go to a destination, so you don't notice the smoking as much. Plus, smoking sections are a concept that exists in the US (even outside), whereas they don't in Europe. Thankfully, in much of the US and EU, most places are finally non-smoking indoors now.

This is a gross overgeneralization. It's different in different parts of the US and different parts of Europe, of course.

(FWIW: I totally agree with you that it's gross. And it's far too common to run into in Europe.)