I would imagine that with Amex failing to renew the 2016 Costco contract. They have to watch every penny now.
Until the realize the real reduction in revenue by loosing one of their largest client bases.

Like many others as soon as the Amex reward card is no longer taken at Costco, I will have no reason to ever need an Amex again.
Unless they can offer a better cash return with no annual fee then the new Costco visa or MasterCard will. And that's highly doubtable.