I'm not up to date on every Des Moines ordinance but I'm guessing that Des Moines doesn't require a parking lot to have a certain percentage of shade. Other cities, for over a decade, require that a parking lot become 50% tree shaded or other aesthetics.
This is an area where downtown Des Moines has never gotten serious. All of the development downtown and this one has missed the boat. The west side of City Hall is postcard beautiful - the east side is a massive ugly -a** slab of an asphalt parking lot. For surface parking lot owners, why not use a carrot and stick? Incentives to help them develop the lots - pressure to make sure they are as pleasing to the eye as possible.
Iowa City: The biggest, best, little city in the Big Ten