They probably were lazy and never got around to doing it, perhaps thinking that using non-lie-flat aircraft on the route would be a short-term, temporary thing. If the route is now CPU eligible while maintaining the perks of being marketed as United Business (i.e., club access in SFO or BOS), then there's nothing to complain about! (Well, except for the loss of lie-flat seating, but that's assumed to be a given in the scenario/question OP was asking.)