Why do we have to eat minerals to maintain our bodies?

Those minerals have different functions. Without iron in your diet, you cannot make blood, since iron is the major functional atom in hemoglobin. Calcium and phosphorus are needed to maintain your bones; potassium is important in maintaining the basic electrical charge in nerve cells.

You can look up the role of minerals in the human diet online...

Why does this surprise you? We are made of chemicals, and we cannot synthesize minerals on our own. (although we can synthesize some vitamins, like D). We also need to consume Vites like C, while my cat can synthesize that. We need to eat food not only for energy and growth, but for the substance of our bones (calcium, phosphorous.....), muscles and circulation system.

I just eat hamburgers