Because Dagg has barely played any 10, and no games starting at 10 in the last 4 years from my memory...
I dont think that's so much of a big deal, Both Dagg and Ben Smith play first receiver a lot in both super rugby and test matches.
Dagg is a bloody good goal kicker too, I actually think he should kick goals more and be more active in that area of the game. He was the regular kicker for the Highlanders one season and basically had the best stats in NZ if not super rugby. would have been a good option in combination with Cruden, Dagg has much better range than Cruden.
picking goal kickers for the situation is something we seemed to have forgotten in terms of the All Blacks. Since Carter has come along the duty has always fallen to the 10 with the exception being in 2011 when Piri kicked goals.
IN a setup where you have left footed kicker (Carter) where its easier kicking from the right side of the field and left side for right footed kickers then Cruden who at times has been accurate from close range but poor from moderate to long range where kickers like Dagg & Barrett are good from long range. I think we should have used our kickers more and let them kick to their strengths.
But back to the subject of Dagg playing 10. The short answer is we dont need him. We have Carter, Barrett, Slade and a couple of viable options beyond that if needed.
Also Tom Taylor seems like a forgotten man, I know he is going overseas but that doesn't matter too much in World Cup year he's still available. He's a bloody good kicker, has the sort of game that is suited to test rugby and proved himself when thrown into a big test match. So there are some things he has over the likes of Sopoanga & Co.