The enforcement is primarily complaint driven. It does catch some legit cases of abandonment, but also sees abuse.

Although the state vehicle code section cited in their paperwork mentions the court, the actual process of dealing with SLOPD or the parking people DENIES access to the court. Appeals go to the same people that issued the towing order.

Except for a home, a car is the largest investment that great many Americans make. There's notice to ones' mailbox before towing. A person that's ill or otherwise not using a car for legitimate reasons may very well not see a notice on the car. The fine is more than that for parking in a handicapped zone or for any other parking violation.
They're unwilling to work with the community to solve problems. For instance I once had someone park across my driveway which is less obvious than most (especially at night) and I called the PD asking if they could help me by contacting the neighbor (I didn't know which apartment he was in) so he could move his car. It wasn't an immediate problem. They said sure. But when an officer showed up, he refused to go to the neighbor and instead had the car towed. They didn't make me happy, and I'm sure they didn't make the owner of the car happy. The solution was worse than the problem.

If they had 72 hour parking signs up and simply issued tickets with the right to go to court, it'd all be fair. But to put someone through some very expensive grief without due process is just wrong. Also, as you noted, the enforcement is spotty. It's often selective enforcement. It may not be bias on the part of an officer, but the complaint process is open to bias too. Someone of lower income with an older car is more likely to be targeted simply because a neighbor doesn't like seeing an older car, or some assume an older car isn't operational.

San Luis has many people that are very environmentally conscious. Many ride bikes, walk, take a bus or car pool. Some students rarely drive except to see family or buy food. Being parked for a period is not abandonment, and the state code used here has no time limit. The city is misapplying the law selectively. It is being applied to some people that have no intention of abandoning their vehicles. There is no opportunity to appeal towing/impound fees at all and only improper means are available (not to a court) to appeal the citation that follows.

Additionally, towing is overkill when in a residential zone. Extended parking downtown (in an area typically metered) reduces availability of parking in a saturated area. But in a residential area, a car that's parked continuously for a couple of weeks versus one that's used a few times during the day has no difference in impact because it's overnight (when essentially everyone is sleeping) that parking is closest to saturation.
Someone towed and subjected to that cost and the impound release fee when it is not an abandoned car will most likely bring it right back to the same area it was towed from. So what's the point of towing?

Beyond simply being parked, there should be some pretty good additional reason to believe a car is intentionally abandoned. Not currently registered, owner failed to give valid address, flat tires... Issue a ticket with right to appeal, send certified mail to registered address... if the car is by the registered address maybe even knock on a door.
The city employees and PD get huge salaries. Perhaps in the things they do they need policies modified to solve problems with the least possible harm. The refusal to knock on a neighbors door when he parked across my driveway by accident makes it clear just how unwilling to help they can be.

You never got cited. If you'd done something (could be trivial - rude when a party gets a noise complaint) they could throw the book at you for other things.
Just laws don't make ordinary citizens into criminals that can be harassed and emotionally / financially damaged with no appeal. (and I said, a neighbor upset with you could easily have caused the same grief, it is often arbitrary enforcement where there is no actual problem)