I think the other issue in the US is the opposite: below a certain density, it's hard for public transit to be effective. Once car-oriented development has sprawled out with suburbs and stroads, the distance between you and a transit-stop is gonna be higher, riders per mile of route will be lower, etc. And when housing prices push people to move further out from city centers (which is important not just for commuting to jobs but access to stores/schools/everything) the problem just gets worse.