Charging a person for space in which to park a vehicle is the easiest way to make money by doing nothing.  It's one of those things that would get me really angry if I thought about it long enough, so I usually just don't think about it.  The thing that's great about paying for parking is when there's absolutely no choice in the matter.  It's not like you have a choice between paying $10 for a good spot, $5 for an ok spot, or $0 for a far away spot.  It's all one flat rate.  This happens with things like baseball games in the middle of nowhere.  There's no possible way to walk there, so every person will inevitably come in a vehicle.  There's no other place to park, so every vehicle will inevitably park at the field.  And instead of including an extra $5 or $10 in the price of the ticket, every carload of people is unpleasantly surprised by the fact that they're forced to pay for parking.  There's no way out of it.  You either pay or you leave.  God bless America. 

Maybe it's similar to why airlines charge for food and headphones.  Giving things out for free means everyone will take it and not think twice about it.  Charging money for it forces people to decide if they really want it, and in many cases they choose a different option, like buying their food from somewhere else or bringing their own headphones.  That makes sense in terms of parking because there's always limited parking.  Charging people for parking forces them to carpool, which frees up spots for more people. 

But in reality, they should just make bigger parking lots or taller parking garages.  Or they should build their stadium right next to a train station.  Either way, being charged for parking is just another reason why many people don't feel bad about urinating and dumping garbage all over the parking lot.  If you're charging money to park there, you surely have people to clean everything up.  What goes around comes around.