I think Alfie has already said it all. He said he doesn't want to be a mentor in his final years in Ottawa (he doesn't want to play second line minutes with rookies)
Also, Alfie is a big union guy and don't think him seeing Karlsson/Turris/Neil/Phillips take millions paycuts to stay in Ottawa (under Alfie's discounted leadership, he is as much to blame as anyone) didn't go unnoticed by him. He played for $1 million last year and was our best player, him leaving sent a message to Ottawa that discounts are no longer the order of business, you want top line players, you have to pay for them like Detroit does.
Alfie said during the previous lockout you have to be happy with the contract you sign, or you can't focus on hockey. He obviously wasn't happy with the contract Ottawa offered so he went somewhere were his only concern will be hockey, no distractions, no retirement talk every year all year, legacy talk, just hockey.