Why do I have scabs on scalp that won't heal?

A part of healing. A scab is a collection of red blood cells, platelets and other things that your body produces to cover a break in the skin. Our skin protects the delicate internal things from the harsh external environment outside our bodies. As the injured tissues under the scab heal. It will eventually fall apart allowing new tissues to fill in the injury. Do not pick/pull at it as this slows down healing.