Of all the kinds of ice cream out there, fruit flavors are certainly the most common — and yet grape is never an option. This can be explained by a few key factors.
Grapes contain anthocyanin, which is hard to freeze. In addition, the acid in grapes spoils dairy, so it has to be removed from grape juice before it can be made into ice cream.
Grapes also have a high water content, and a watery base will make ice cream with chunks of ice. While the technology to make it happen is out there, the demand is not high enough.
There is also an ongoing rumor that the FDA banned grape ice cream for the danger it poses to dogs, but this story is unsubstantiated and is more of a fable.
Though grape ice cream being made on a commercial scale is unlikely, you can make it yourself by boiling grapes to make grape syrup and adding it to condensed milk and cream.