Probably because that senior FO takes a vacation bid from another FO. Takes a very good line then gives it away and flys cpt trips and also takes a spot away from someone who wants to upgrade for technically forever until it was changed to one yr max.
The purpose for the lance program is no longer there. We have plenty of guys who will upgrade and aren't short captains that we cant make.
Still if given the opportunity and I want to wait that long I'd lance for a yr.