My followup question that may not answer anything but may narrow the search is. What were the hairstyles of the franks and what were the hairstyles of their Scandinavian ancestors at the time?

According to this French source, it was a stylistic issue, having to do with aesthetics and notions of masculinity. All of the Frankish regions wore their hair "nuque rasée" as well. It may also have symbolically distinguished them from the "Sarrasins" or Muslims met in the Crusades.

http://www.normannia.eu/pages/histoire/la-coupe-de-cheveux-dans-la-normandie-du-xieme-siecle.html