Human bodies work in weird ways. Some parts heal easier than others, while others don't heal at all. Amongst these that don't heal are teeth. Teeth can heal themselves to a certain degree. But since they lack the right cells to do so, they have no opportunity to do so against visible caries.
“Cells are what start the healing process in our bodies, and as tooth enamel consists of 90 percent minerals, there aren’t many proteins and cells there,” educates Janne Reseland, a professor of biomaterials at the University of Oslo. She states that at the baseline of the roots of teeth, we have cells that can offer a certain extent of repair, but not up in the crowns. Morten Rykke, another professor of Cariology at University of Oslo states that “Acid damage is our biggest dental headache today – more so than sugar and caries!”
Enamel is a solid crystalline matter which does not have any inner or outer blood supply. The body has no way to transfer the healing resources to the impaired area. We are by nature, given 2 sets of teeth. They are the primary (baby) teeth and our secondary (adult) teeth.
A fun fact you should know is that sharks have the skill to form new teeth as required to shove out damaged teeth. However we as humans have to stay with our chipped teeth for the rest of our lives.