Comment by throwaway0a5e

There are some towns where the police have so little headcount that they have enough "real crime" to keep their officers as busy as they want to be and so unpredictably the officers would rather bust drug traffickers and respond to violence than write tickets. These tend to be poor urban communities where the cops (very much like teachers) only work there for a short time early in their careers.

But yes, in the general case you're right that law enforcement is a revenue generator.