Maybe they think that if you're there already, you know. :)
It's odd given the estate's seeming insistence on The Gershwins' Porgy and Bess that they don't show it that way on the home page ad for the Met production.
And if you click to get licensing info, you ultimately go to the Concord Theatricals site, where the title is listed simply as Porgy and Bess.
I haven't been to the Met production. What does it say in the program? On the Met's archive pages, it's listed just as Porgy and Bess, but the page specifically for the current production says The Gershwins' Porgy and Bess.