Many people don’t get enough vitamin D in their food. They still get enough vitamin D, because ultraviolet radiation creates it—usually.
If you’re as fair-skinned as the average northern European, you only need about 20 minutes per day. All you have to show is an area of skin about the size of your face.
Without vitamin D from sunlight exposure, lactose assists with the use of calcium. So, cultures with easy access to leafy greens plus sunlight or fish, calcium is taken care of and milk has no advantage. Cultures without access to leafy greens, sunlight or seafood need dairy either as a source of calcium, lactose, or both. You can read more about it in a previous post.