There was a thread
a month ago about George Lucas "morphing" two different Hayden Christensen performances together because he liked the merged performance better than anything the human actor provided, and then he composited it into a scene in Episode 3 (where Anakin wasn't even the main focus).
Posted in that thread was a
behind the scenes clip of Episode 1, where George plays "create a shot" in the editing room and mixes and matches individual actors performances using compositing.
He absolutely could have made one clonetrooper costume and had one extra play five-to-ten clonetroopers. But why hire an extra for that when you can just build a goddamn robot in your computer and it acts exactly the way you want it to act. George hates actors. He thinks they're an unwanted obstruction standing between his script and the camera lens. Why wouldn't he replace faceless stormtroopers with CG. I'm surprised he didn't replace C3PO with CG. Oh, wait...