There are a few possible reasons for why James Caan ends his tweets with end of tweet. One possibility is that he wants to make it clear that he is finished with his thoughts on the matter and doesn't want to leave any room for misinterpretation. Another possibility is that he simply enjoys the symmetry of having end of tweet as the last thing he says in each tweet. Whatever the reason, it's become something of a signature for Caan and helps to set him apart from other Twitter users.