Why the wine ads don't mention the benefits of resveratrol.

They don't want to litigate:

In 1991, some aggressive winemakers sought to trumpet the health benefits of wine, but they were quickly shut down by the Bureau of Alcohol, Tobacco and Firearms, which then regulated the industry at the federal level. Even the industry’s trade organization, the Wine Institute, counseled against promoting wine as a health drink....

“We put on a back label, that wine is healthy and recommended in the Bible,” [Michael Mondavi said]. “The B.A.T.F. sent us a cease and desist letter and made us change the label even though we went back to Washington and showed them the scientific evidence and read them the Bible passages.”

The article doesn't identify the passages. There's this:

Go, eat your food with gladness, and drink your wine with a joyful heart, for it is now that God favors what you do. Always be clothed in white, and always anoint your head with oil. Enjoy life with your wife, whom you love, all the days of this meaningless life that God has given you under the sun— all your meaningless days. For this is your lot in life and in your toilsome labor under the sun. Whatever your hand finds to do, do it with all your might, for in the grave, where you are going, there is neither working nor planning nor knowledge nor wisdom.

And this one, which is less grand but actually makes a health claim:

Stop drinking only water, and use a little wine because of your stomach and your frequent illnesses.