In Byzantium during the era of Justinian I, despite the difficult wars, there was a flourishing of culture, and in the West

In Byzantium during the era of Justinian I, despite the difficult wars, there was a flourishing of culture, and in the West – cultural stagnation. How can this be explained?

In the VI century in Western Europe there was not stagnation, but the absence of folk culture, since the Roman people had already disappeared, and new peoples (French, British, Germans) had not yet formed. They were formed in the 9th-11th centuries; shortly thereafter, medieval civilization flourished.