I think he really hit the nail on head here:

"Part of this is a result of poor planning and ordinance-making that long ago overcompensated for the wide use of automobiles. Henry Grabar, a staff writer at Slate, mentions this in a book published last year, Paved Paradise: How Parking Explains the World. ”On a national level, certainly, there’s far more parking than we need,” Grabar said in an interview. “There are at least four parking spaces for every car, meaning that the parking stock is no more than 25 percent full at any given time. And some of those cars are moving at any given time, so parking may be a good deal emptier than that.”