Cold towels on the head is to lower brain temperature while allowing the fever to run elsewhere. Brain tissue is much more susceptible to thermal damage than the rest of the body.
Surface cooling of the scalp seems like it'd have a very limited effect on cooling the brain when body temperature blood is being pumped directly into the brain.
Source: https://www.wemjournal.org/article/S1080-6032(14)00405-0/abs...
Cold towels on the head is to lower brain temperature while allowing the fever to run elsewhere
It still seems that if the goal is to cool the brain and not the entire body, cooling the blood on its way to the brain is better than surface cooling blood in the scalp that's going to soon leave the head through veins.