I don't really understand the question. The implication here is that the Byzantine Empire didn't preserve Roman culture when the evidence clearly indicates Roman culture WAS preserved throughout the history of the Byzantines.

Lars Brownworth talks about this in the opening to his book, Lost to the West, "What we call the Byzantine Empire was in fact the eastern half of the Roman Empire, and its citizens referred to themselves as Roman from the founding of Constantinople inv323 to the fall of the city eleven centuries later." Allies and enemies alike considered the Byzantines to be Roman-- because they were. Emperors in Constantinople traced their lineage back to the founding of the Roman Empire by Augustus.

Emperors in the East spent generations upon generations trying to retake the lands lost by the Western Empire. They were successful at times, retaking some land lost and holding it for quite a while. Byzantine ships landed in Byzantine ports in Italy until the 11th century. The empire saw itself as the other half of what was lost in the West in 476 ACE. Constantinople was always Roman in their eyes.

It must be noted that these Roman ideals that were preserved were Greek oriented rather than Latin or Italian oriented. The greek flavor of the court at Constantinople wouldn't seem that out of place in Rome a few centuries earlier, but it wasn't exactly the same. The ideas of law and order and justice founded in Roman times remained. A strong central government ran by an Emperor remained. An appreciation for the arts remained. An appreciation for Greek philosophy and literature remained.

The only way in which Byzantium didn't preserve Roman culture can be attributed to the slow grinding of time. From the founding of the Roman Empire to the fall of Constantinople almost 1500 years passed. It's difficult for us to realize just how large an expanse of time the Roman Empire existed when you take the Byzantine Empire into account.

Any culture will change through the centuries and the fact that the Byzantine court of the 14th century resembled in any way the court of Rome is remarkable itself. Brownworth again remarks at what he found in his study of the Byzantine Empire, "I found myself confronted with a rich tapestry of lively emperors and seething barbarian hordes, of men and women who claimed to be the emperors of Rome long after the Roman Empire was supposed to be dead and buried. It was at once both familiar and exotic; a Roman Empire that had somehow survived the Dark Ages, and kept the light of the classical world alive." The fact is that cultures change over time, based on the influence of neighbors, changes in religion, defeats at the hands of enemies as well as a dozen other potential factors. You can't really blame the Byzantines for being different from Romans. It would be like asking why didn't we as [insert nation here] better preserve our culture from a thousand years ago? How can you?

So I would say that, although Byzantines and Romans weren't exactly alike, it's remarkable that a culture was able to survive for what amounts to the better part of 1500 years.

Brownworth, Lars. Lost to the West. New York: Random House, 2009