..I got a better question, why should Sorcerer's get Influence for a skill? They're magic is based on raw power and emotions, experience by doing and what not. No study involved what so ever, say for seeing "Wat dis power do".
The reason other classes have influence is due to being quasi-social characters within a city/organization. Sorcerer's are a far cry from a Noble bright paladin, an orderly and wise monk, the cunning urban rogue, or a bard who plays to others egos.