This is a very inexpensive form of public transportation that just happens to provide a myriad of health benefits.  Clearly, it is not meant to be an alternative to walking but rather an alternative to driving or catching a bus/cab/uber/etc.   The year-round heat also makes walking more than a few blocks undesirable... ultimately forcing most people to use their air conditioned cars, etc.  Cycling creates a natural cooling effect (i.e. 10-15 mph breeze blowing over you constantly) and is more desirable over walking especially in our hot climate.