It more then likely has to do with his family not originally being from the New Orleans area, most of his family is from Mississippi, so i'm sure growing up and on a regular basis the people around him talked a little more country(like Archie), plus the fact that he went to Newman which is considered a very upper class school and generally that New Orleans accent isn't really going to be there.
The thing about Eli and Payton to me is their accent isn't New Orleans but its also not as thick(Mississippi country) which explains the above situation to me....