I would guess that as missionaries brought Christianity to the northern tribes (Germans Slavs et al) they presented a Jesus that looked like them.
Yeah, that makes alot of sense to me. Not that it really matters what he looked like, or whether certain parts of the mythology were inspired by earlier dieties, or even the role of Mary Magdalan. All that should really matter is the teachings and message of Jesus, which unfortunatly seem to be missing today. But that’s just my viewpoint as someone who doesn’t get involved with organized religion.