Why do head and scalp wounds bleed more than others?

Many blood vessels. The scalp has ac very rich blood supply. It is easy to cut or tear its full thickness with a good chance of damaging many small vessels or a fairly major vessel. In addition cut scalp vessels tend not to retract as cut vessels do elsewhere, thus eliminating the first step of "hemostasis" (the body's natural mechanisms of stopping bleeding).
Blood supply. The scalp has a very rich network of blood vessels.