If that was the case, then all their deals would have to be the same if offered at a certain price.
It's like offering sakura and both blooms at 2500, but then offering kerria and both blooms at 3000 if they didn't keep the same price. A player having both is essentially paying 500 more for what's practically an exchange ticket and both blooms on both deals.
Sure a smart player would pay attention, but who's to say they wouldn't offer a cheaper one later at 2000 or something?