I think people associated Mafia with organized crime because of leaders of the Commission, figures like Al Capone and John Gotti. The Mafia got an special kind of mystic figure about it. Thats why, everytime you got an organized groups, the media try to put mafia behind it, because Mafia = highly organized crime.
Also, groups want to be associated with the mafia, because the mafia look more like an entreprise than a gang. People still thinks that a made guy is always in suit, even when he sleep.