Marriott has introduced a RC branded version of Marriott Rewards and an associated credit card. Inasmuch as Chase is the issuer of that credit card, and is locked in a market share battle with American Express, it's not surprising that Marriott would now be "unhappy" with their relationship with American Express.
This could be a big part. For Centurion members who lost SPG Platinum and Continental Gold Elite of late losing the extra $50 credit and time of booking upgrades with Ritz would really devalue the Centurion card.