Why are bodies made up off specialized cells?

because a body is more efficient when it has specialized cells. The human body for instance has many types of specialized cells. the neurons (brain cells) perform a different function then skin cells. This specialization allows for complex life beyond single celled organisms because not every cell has to catch nutrients from the environment. Since very few of your cells actually work on absorbing nutrients from the environment, they can focus on other tasks, such as holding your shape (bones), thinking (brain cells), etc.