Budget projections - learn how they work, and why they have estimation plans well in advance. It is about money. They order cars, construction of jails, etc. on budget projections. Then they have to pull in enough revenue to make those budgets. This is not the federal government. City, state, and counties, are supposted to not run a deficit - by law.
Tickets bring in a lot of revenue.
There are enough people committing crimes that require an arrest - that is why jails fill up. Look at their budgets though - guess where a large portion of the jails budget comes from.