Current local parking example is a new apartment block - ~500 units, ~800 spaces required, developer thinks ~600 is enough because the building is adjacent to a subway stop and across the street from a massive mixed development. This is an area with almost zero on-street parking - there's no risk of tragedy of the commons here because there's no street parking to "steal".

Why is the county requiring more parking than the market value? The developer has no incentive to under-build parking - nobody would rent in the building if there wasn't enough parking available.

Edit - Des Moines has 19.4 parking spaces per household. Seattle has >5 per household. Other stats about parking density in the article...

https://www.fastcompany.com/90202222/heres-how-much-space-u-...

> The developer has no incentive to under-build parking - nobody would rent in the building if there wasn't enough parking available.

The very existence of slums/slumlords suggests that selling substandard housing to desperate people suggests both that there are people willing to accept substandard housing and that it is profitable. If it can work with rat and mold infestations, etc, it can work with an uncomfortably small amount of parking.

I have no idea what the right amount is, but I certainly don't believe your reasoning provides more information.