Earlier quoted context omitted.
The Police Chief lost his job over it. What other consequences would you think appropriate?
Investigations and penalties for everyone up the chain, starting with the frontline officers who were on the ground refusing to issue tickets. If an officer chooses to not do their job over their political beliefs they do not belong on the force.
Same applies here. If 10 officers misbehave, it is easy to fire them all, as you suggest.
If a majority of the entire police force defects, your only choice is between limiting the scope of the punishment to a few ringleaders vs. basically disbanding the police force and starting a new one from scratch, hoping that you can even recruit enough people to do so; but, in the meantime, the city won't be policed anymore, as the entire institutional memory has been purged.
In most similar cases in history, the authorities opted for a blanket pardon, as it is much less of a headache.
It is not even a new problem. Police is a relatively recent institution, but armies, gendarmes, legions etc. rebelled all the time, and peace usually had to be bought by concessions.