With the exception of AC's recent change to seat pitch in the first economy rows of much of its narrow body fleet, Preferred seating was nothing like UA's E+ and there's no reason why UA should be giving away E+ seats to other STARGolds since it is a genuine enhanced seat. AC is now only giving the true improved Preferred seats to upper tier elites, others must pay for it, just like UA's policy. The only benefit of Preferred seats on wide bodies and other unenhanced aircraft is being in the front of the back cabin, thus getting off the plane sooner and having your meal choice before its taken by everyone in front of you. Many STAR carriers permit STARGolds from other programs to take seats in this type of forward economy cabin thus the reciprocity here. But E+ is not this type of seating so no reason to reciprocate.