I'm too lazy/cheap to revive my P.O.S. Car, too poor to buy a newer one, and fat enough to need
the exercise.
The environmental/energy concern factors in there somewhere, but thinking about all the oil/fossil fuels it took to make any given bike starts making that one a little dodgy. yes, its far less resources than it took to make my car, but might still be enough that giving a bike to everyone on the planet would be resource prohibitive.