Except that many/most local governments are in turn covered by insurance. So suing them is not fundamentally different than suing a private citizen with similar insurance. Both costs are born by the pool of insurance purchasers, private and public.
The insurance is likely owned by "us" anyways through our mutual funds, retirement plans, etc. And high insurance fees come out of our pocket directly as well by making such policies more expensive in the next city.
The issue though is that it's not the pockets of the guilty. Officers are almost entirely shielded from the legal and financial costs of the damage they do.
When we ask "Why do they behave like that?" the answer is because they can, and there's literally no reason for them not to. They're literally consequence free.
They don't pay a bit. We, on the other hand, pay and don't receive value for our money.