Maybe it's not that bikes are more convenient, but cars are more inconvenient in areas where bike use is popular. I am thinking of densely populated areas with expensive real estate like NYC and the Netherlands. In these areas, high priced land is less used for streets, parking lots and garages. Consequently, more people are carfree because it is very expensive to store cars, and narrow streets become too congested when a lot of people drive. So many more people don't drive, and some of these select the alternative of using bicycles.