Most players of Bell's status won't play on one year deals. I believe it's rare that teams franchise players in back to back years. There are future millions on the line for players of Bell's status. Teams will either sign them, trade them (I think this is rare), or let them hit free agency. Bell doesn't have to sign his franchise tag until X amount of games(not sure how many) into the season to get credit for the entire season. He takes a risk by even being there for the X amount of games. Ultimately would you risk being injured in camp with potential millions on the line? I wouldn't. That would be a bad business decision. Bell's playing by the rules.