He can't win the nomination, but that's not the game he's playing.
He's trying to siphon off enough support (financial or otherwise) of social conservatives to de-emphazie that voting block for the party insider's preferred candidates' benefit. The longer he stays "viable", the more "good" he can do in that regard (and self-promote his next book and to-be-resumed FOX News show, I'm sure).
By pooh-poohing the straw poll, a poor result (which he likely would have gotten anyway) can just be dismissed because he wasn't trying to win it.
Good analysis. I think you are right.