The city itself would be losing that revenue if it retained control, and even with the deal they still need to budget the loss in parking ticket revenue.
The primary reason the parking deal never goes away is that it allows the city to blame "investors" for doing something it was already wants to do (keep lots of street parking).
> The city itself would be losing that revenue if it retained control
Ok but as an urban planner it's a whole lot easier to tell your boss "hey we're removing 5 parking, spaces we'll lose x dollars per year in parking fees" than it is to say "hey we're removing 5 parking spaces and we need to come up with $5 million to pay the parking company"
The primary reason the parking deal never goes away is that it allows the city to blame "investors" for doing something it was already wants to do (keep lots of street parking).