The voters don’t know when police are overstaffed, that’s the problem. Only police management understand how over-subscribed officers are and they have no incentives to fix it when there are too many officers for what’s really needed.
You live in a fantasy if you think voters make rational decisions about policing based on police-load.
They get given money by government, representing the voters.
If the voters think they're happy with less police of course they can drop 100 employees worth of budget. The police can't stop that.