A parent, whose child may have difficulty comprehending a basic picture book or may just not be grasping the nuances of word problems, may not see the need to stop and talk about the colonization of America, or the function of the human heart.
Whether in public school, where the priority of these classes are often shuffled aside for focus on the "3 R's", or in a home-school situation, struggling kids, often find themselves at a deficit in the areas of comprehension and knowledge.
What are you really teaching when you teach the cycle of a butterfly, or how a bill becomes a law? You are giving a child vital knowledge of how our world functions. You are giving that student information that they can apply to new situations, and can give them a foundation of learning that they can apply new learning to. Many core reading comprehension issues start out as a knowledge deficit issue. You want your child to have a leg-up when it comes to living and independence? Science and Social-Studies teaching are vital ingredients.