In this case it is though.
Its very simple - Under the tag he was guaranteed 14.5 (or whatever amount it was) for one year. Thats it. Nothing more, nothing less. If he gets seriously hurt then he is basically done. Not too many 29/30 year old running backs who have been hurt get contracts in the league. and yes, i understand that this is the most extreme case of "what if" ... but players have and do get hurt doing the stupidest of things, let alone the inherent risks they take when playing.
So Bell sat out a year... he lost out on 14.5 million dollars. He will never get that money back. But, if he gets hurt, he gets to keep the guaranteed portion of his new contract. What would you rather have? 14.5 or 31.5 million? So by sitting out a year, he has guaranteed himself 31.5 million dollars... to me, that's a win. ymmv.