>>212995422
There are many factors but I think one of the main ones is that our country is relatively sparsely populated aside from the medium/large and dense cities, which means building infrastructure between cities is very cheap (you don't have to navigate around massive suburbs and evade countless tiny towns). Pic rel.
On the other hand dense cities means it just makes economic sense to develop infrastructure inside them such as metro lines, as each km of metro built will get you far more benefits than in other less dense cities.
There are a few other aspects like how the contracts and budgets are awarded and structured but I can't really talk about those points because I'm not familiar with that.

>What's the most nonsensical thing about European population density to you?
wtf is wrong with us