I believe the overarching goal is to prevent the neighborhoods from becoming ones where there are two cars parked visibly in every driveway. The city desires that cars are stored out of sight or attractively under a carport. I don't think they'd approve a permit for a plain ugly covered parking structure that sat over the driveway area (not compliant with setback rules at least). As such, you end up with either cars in garages, parked out of sight behind the home, or in an attractive carport adjacent to the home (which probably only allows a single car). Cars parked on the street have to be moved every 72 hours, so that's not an option either.