The Normans are a bunch of Vikings that settled in northern France, and within a century they were Christians speaking French. By 1066 they had become very experienced at fighting wars between themselves, a skill that came in useful, but they also produced magnificent cathedrals across Normandy and later, England.
So where did this come from? Did the rich Norman lands attract experts from across Europe? If so, why didn't they also go to rich Anglo-Saxon England?
Was it just a fashion that happened to catch on there?