Grapes for winemaking tend to have thicker skins than grapes for eating. Thick skins aren't fun to chew through.
But winemakers like a nice thick skin, because that's where a lot of the flavor & aroma compounds in wine come from. They're in the skin, not the inside of the grape.
Vineyards for wine grapes can be surprisingly, uh, not as lucrative as we might think.
Grapes for eating fresh tend to command a higher price. Why?