The question is, what kind of parking? A lot of the available parking is in structures that cost to park in, and involve some overhead getting in and out, such as getting through a gate, wandering around the structure for an available space, etc. Not conducive to being used by an Uber or cabbie to wait for a call to go pick someone up. Finding on-street parking is much more dicey.

The commuter and residential parking doesn't free up for Uber drivers if it's not being used by its primary customers.

Disclosure: Extrapolating from how it works in my town.