We can see here that the reason Faber does not want to help Montag distribute books is: Faber has already tried to help society and failed.
Faber is reluctant to assist Montag because he has previously attempted to make a difference in society by preserving and sharing books, but his efforts were unsuccessful.
He feels disillusioned by the lack of impact he made previously and is hesitant to involve himself in another potentially futile endeavor. This reluctance stems from Faber's past experiences and the sense of defeat or disappointment he feels due to his previous unsuccessful attempts to make a positive change in society.