You can add Marriott shopping. Link your Rewards card and start earning. We joined AAdvantage and Delta ski miles, we get more mile by purchasing stuff than from actually flying. Bottom line is it all adds up to free hotel rooms, or free air, or both; and they recognize your elite status.
I have both the Marriott Visa and Delta American Express. I use the Delta card for everything relating to flying and am quickly on pace to close in on a medallion level, and since I have reached Platinum Elite with Marriott, I still use the card, and Marriott is good at telling you about programs where if you stay 15 times in the summer, you get 25,000 points or something like that, so it pays to continue to use both, when you buy items and when you travel. Loyalty should be rewarded.
Now if both Delta and Marriott can allow for use of each other's cards to accelerate my points on each other's platform, I'd be ecstatic!