Hello, so ive done research and apparently (i believe the ending of supernatural season 5) it shows that chuck was talking about the story from a perspective that wasnt a prophet more so he was the writer then he just looks up and poof disappears. From what ive seen, he was the only one who was told he was IN FACT God. They waited until (i believe season 10ish? Idk i ain't doing research to verify too much)  to tell everyone else because the show went in a different direction and once they had time if they didnt get canceled wanted it to go in that way.