Maybe it's too expensive ($88 a year versus 30 for Vélib in Paris), or maybe it's also a matter of urbanization : european city have a bigger population density

Maybe it's too expensive ($88 a year versus 30 for Vélib in Paris), or maybe it's also a matter of urbanization : european city have a bigger population density than US ones, which makes it easier to commute with a bike because the distances are smaller. (In Paris for instance you can almost go from any point to any place in the city with the 45min extended plan (40€ a year)). I don't live in Paris anymore but I still go there several times a month and even now owning a Vélib pass is a no brainer.