First- Yea, the Steelers offered him a good contract- but the contract they offered (even the Franchise tag) is less than he would get in the open market.
Second- You dont trade one of your best players. Like it or not, the offense goes as Leveon goes. You really think its easy to replace a franchise player like him in FA or the draft?
He is a great running back, no doubt, one of the best in the league. But I respectfully think you're overvaluing him. I don't believe the offense goes as Leveon goes. I think you could still get very good production from a number of decent backs. Brown and especially Ben are MUCH more important to the offense. And fine, trade him to a team that will give him what he deserves. The fact is, the Steelers have been MORE than patient with him throughout his career. Multiple injuries, suspensions, etc, and he repays them like this? He's great, but he's not THAT important. And his BS will hurt the team.