The Greeks studied from the earlier Minoan and Agean arts and developed their style from there. They were master sculptors who idealized the human form because of the philosophy that humans were in the form of gods and the perfect creation of gods. Their drawing didn't develop with realism until the later centuries, not out of lack of skill but out of the slow evolution of artistic style and what was seen as beautiful--you can't break the art rules too much in ancient Greece without blowback!
The Roman masters studied from the Greeks--they were OBSESSED with Greek art, and that's not an understatement! In fact, most of the "Greek" marbles that survive today are actually Roman copies of Greek sculptures that were originally cast in Bronze (a different material entirely). In the late eras of Greek and Roman civilization, these precious sculptures had been melted down for their much needed metal on the war-fronts, and so only the marbles survive.