Why was Luke The Lightning Thief not Ares in the Lightning Thief movie?

Answer 1

Luke is a major part of the plot of the entire series while Ares only plays a minor part in The Lightning Thief and a part about as big in every other book in the series. If you look closely Ares was in the movie, just he didn't have an obvious role; he was at Olympus and could be seen if you looked very closely when Percy returned the bolt to Zeus. PLus Luke actually was The Lightning Thief in PJO: The Lightning Thief but Ares took it from Luke while Luke was on his way to Kronos (or Cronus, your choice.)

The book states that gods were not allowed to steal from each other, and with Zeus being who he was, would you? The book also says that the gods often got heroes to do this kind of thing for them. That's why Luke stole the lightning bolt and not Ares, and why Percy had to get it back instead of Zeus or Poseidon.