because the mafia, the name that is commonly used to describe the italian organized crime syndicate, has been historically against letting minorities, or any non-italian, into the families.
it's hard for me to believe that an organization who has been at odds with minority gangs for the past 20 years due to similar business interests would have an entire family of black mafioso.
unless this is just a phrase used by a group not affiliated with the sicillian rooted mafia, using the mafia name as an easy way to show the world what they think of their toughness and savvy as organized crime members.