According to Jason Cole of Yahoo! Sports, one of the reasons the Steelers don’t want to bring Harrison back is due to some concerns over his attitude.
Another reason Steelers won't re-sign James Harrison is that they're concerned his attitude will be bad based on how situation has unfolded.
— Jason Cole (@JasonPhilCole) March 26, 2013
Harrison has a history of telling people how he feels and I wouldn’t be shocked if he gave the Steelers an earful if he was re-signed.