Answer:
Well, for one, religion has changed, as well as the practice of those religions. Christianity and Islam, the world's largest religions, did not exist/rise to prevalence until just prior to the Middle Ages. The changing nature and expression of religion would certainly cause differences in art expression. Certain religions were also oppressed through the eras you've mentioned, and oppression and fear are powerful emotions that would also influence art. There are a million different factors that go into this, but I hoped this helped a little.
Step-by-step explanation: