A waiter/waitress serves individuals as the primary purpose of their job. They make about $2.50 an hour with no benefits, tips being their primariy income.
Police officers serve the community, not the individual. The make a good deal of pay with benefits. If you tip a police officer, it benefits you, often to the detriment of the community.
A mob boss tipping a police officer = crimes more likely to be successful.
A mob boss tipping a waiter = no spit on the burger.