> Parking spaces are a public resource. The city sets tariffs at a level it feels reasonable.

Particularly, while the tariffs are intended to provide revenue they are mostly intended to supplement hard time limits in providing an incentive to limit how long you spend in the space, and largely are intended to be low given that purpose because they (and the hard limits) exist to enable commerce by encouraging turnover and thereby providing accessibility.

Maximizing fees by using an auction mechanism would not serve that purpose.