Looking at population density if you draw a 50km radius in the Netherlands you get about 8m people. This covers lots of small cities etc. In the US you get maybe 5m in a contiguous city like Phoenix (which fills the circle) or the Bay Area. (LA is more dense and you might get 10m.)
Transit works much better in the Netherlands and much of Europe because those homes and job centres are not as evenly spaced as they are in most American cities since they developed more around public transport existing. S the effective density experienced is much higher.