While the racket system in Mafia 3 was repetitive and tedious, I find a secret genius beneath them. They're all connected in some way like Smuggling brings in the goods, Contraband stores them, then they get sent to the Black Market.
Also the rackets fits each underbosses personalities:
Ex. Roman Barbieri is the head enforcer so his rackets are simple yet effective and involve strong arming people. Moonshine and Protection.
Ex. Tony Derazio is the accountant, psychotic yet sophisticated, so his rackets are more white collar. Blackmail and Construction.
Ex. Lou Marcano is a people person so his rackets involve getting people what they want. Sex and Drugs.
Ex. Tommy Marcano prefers to keep a low profile so his rackets are more low key. Black Market and Gambling