Why does second degree burns hurt more than third degree burns?

 Third and fourth degree burns may not hurt because the nerves are destroyed.

Second-degree burns (partial thickness burns) affect the epidermis and the dermis (lower layer of skin). They cause pain, redness, swelling, and blistering. Third-degree burns (full thickness burns) go through the dermis and affect deeper tissues

in second degree burn the nerve endings are exposed and not destroyed however in 3rd degree burns it is totally destroyed by burn so it is not painful

Completly agree. In the third degree burn injured the skin nervs terminations are destroyed and therefore there is no pain sensation. But it does´n meen the patology in not severe, to the contrary,,,is more severe than a second degree burn injure,,,depending of course of the extention in corporal surface.