I would argue that most of those 600 million are not "parked for too long in one place", which is what I said is not enforced.
The vast majority of them are likely the ones that can be verified on the spot -- things like being parked in a no parking zone (whether street cleaning or regular), expired or hasn't paid parking, etc.
NYC has alternate side of the street parking on most streets which means that for a two hour period, typically midday, on Mon/Thu or Tue/Fri. This has the effect of making you move your car every 72 hours, and it is trivially enforceable. Additionally there are 1 & 2 hour spots which are typically metered.
The vast majority of them are likely the ones that can be verified on the spot -- things like being parked in a no parking zone (whether street cleaning or regular), expired or hasn't paid parking, etc.