As I posted in the SD spoiler thread, Vince has no faith in Christian and loves Orton. Why? I wish I knew that answer. Like Most here I like Christian he is definitely paid his dues and how do you know if a guy is a draw unless you give him a chance to be a draw? Orton is more boring than watching paint dry. His matches lull me to sleep.
He's WWE's 'safe' option. They know he's one of their bigger names and a guaranteed draw (to a certain extent). Not to mention merchandise sales. He's a little like Cena in that respect.
Christian is probably seen as more of a risk to WWE. Whilst over, he's not quite as established as Orton. It's stupid though, since if they don't ever give him a title, how do they expect him to ever progress? (unless they don't, of course.)