Most urban parking structures/lots in the US seem offer so-called "early bird" discounts for parking, where a substantially discounted flat rate applies to customers entering before a certain cutoff time (typically 9 or 10 AM) and exiting before late evening (typically 6 or 7 PM).
The practice is nearly universal, so there must be some economic advantage to it (unless the various players are locked into some kind of weird Nash equilibrium).
My best guess is that this is a kind of price discrimination targeting people commuting in to work, but price discrimination usually soaks business customers in order to offer discounts to discretionary customers, and this situation is the opposite, so I'm not sure that's it.
It could be that it's especially valuable to kick out a large number of vehicles by early evening so that a "second crop" of customers can be brought in. But evening rates (at least when no special events are being held nearby) are also typically discounted.
It could also relate to minimizing turnover costs and traffic congestion. But turnover costs for a parking lot (especially an automated one) seem to be a tiny fraction of the overall cost.
And it could be the result of a price war between suppliers. Knowledge of a particularly cheap nearby lot would tend to spread quickly among coworkers.
Is there a definitive slam-dunk reason these discounts exist?
EDIT: Another guess is that commuters are high-knowledge customers and shoppers are low-knowledge customers and so it makes sense that the latter would tend to get charged more.