I'm going to be honest.
Bully is nothing when compared with other R* titles.
People love it yes, but Rockstar are a business.
A business loves money.
What are Rockstar going to do more likely, a 2nd Bully game or a 4th Red Dead game*?
Despite Bully being released on 5 platforms (PS2, Wii, Xbox 360, PS3 Market, PC) it didn't outsell Red Dead.
(The 3 Red Deads: Revolver, Redemption & Undead Nightmare)
Rockstar hasn't forgotten Bully's existence though, a few months back they had a "throwback jobs" post where they posted player created themed jobs from San Andreas, Red Dead and Bully.
Obviously, the SA themed matches were around the ghetto areas, RDR's was in the desert and Bully's was by the university/college.