There's a
Thrifty Traveler article with a quote attributed to Delta:
Due to decreased demand of these travel-related benefits and as we look to reduce costs to focus on our core business, SkyMiles Select will be suspended starting April 1. We’ve received great feedback from customers on this test and we’re sorry for the inconvenience.
I suspect it was due to alcoholic beverage service being suspended... I think it will be back, I just wish the benefits were slightly better, though it does have to occupy an odd market segment that it shares with the Delta-branded Amex cards.