There's cave drawings from people who lived in Europe thousands of years before the invention of farming, the animals depicted are extremely realistic looking. Then you had the Minoans and Etruscans and the Greeks and the Romans and probably a bunch more than I'm leaving out. Their paintings are extremely realistic looking.

Then the Early Middle ages start and art becomes very very different in Europe

For 1,000 years, until the end of the medieval period, art has a vastly different style. Then the Renaissance comes and are changes drastically back to a very realistic style.

Are there any known influences on the preference for why are changed so much? Are there any theories about what possibly could have happened to influences people's preferences in art so much?