Cambridge takes in $5.5M in Parking & Traffic fines and spends $10.2M on parking management (https://budget.data.cambridgema.gov/#!/year/default). A lot of people think that cities rake in cash from parking tickets, but parking enforcement really doesn't pay for itself. The reason cities do it is because the alternative can be more problematic. Imagine the cries from residents complaining that out-of-town people are taking up all the parking on their street. Imagine the cries from businesses complaining that a few residents are taking up the metered spots in front of their shop so no one can get to their shop (ignoring the fact that most customers in Cambridge wouldn't be coming by car anyway).

Everyone hates aggressive enforcement, but they also hate parking being unavailable.