Robbie doesn't play anymore because he isn't good enough, its really that simple
his scoring rate is lower than every main striker who has played for Spurs in the last 3 seasons outside of Crouch, who isn't played because of his goal scoring ability.
There have also been stories the past year or so about his attitude in the dressing room, and his attitude on the field when he throws a tantrum every time someone does something he thinks was wrong doesn't help as well
He is the 4th choice striker on the team, and with regards to current form/talent that is where he should be. If people still thought he was good enough he would have been picked up in August by a team needing a striker for the 8m or so Levy wanted for him