So Rupert got immunity again, which is very surprising at first glance, considering the number of people who have had discussions during this episode about getting rid of him. On closer inspection, though, it makes a little more sense. Suppose that going into this challenge, Burton and Lill hadn't yet had the opportunity to secure the votes of Tijuana and Darrah -- either because it just wasn't done yet, or because the Morganite women were still feeling like the safest bet was to go along with booting Ryan-O. This makes sense to me partly because Burton seems to have known going in that they were taking out Ryan-O this week; Lill wouldn't have coconutted him twice, including knocking him out of the game, if they hadn't already agreed with the rest of the tribe to go after Ryan-O. Ryan-O's relentless early coconutting supports this theory too, I think. It was a done deal at that point. Furthermore, some supplemental material that showed up after the show indicated that Tijuana was pretty pissed off at Ryan-O by this point, and she may have just wanted to persist in getting rid of him.
So if we assume that the Burton/Lill/Jon group hadn't yet cemented its alliance with the Darrah/Tijuana pairing, then everything that happened makes sense. Darrah and Tijuana certainly wouldn't have wanted to risk pissing off Rupert, lest he boot them before Ryan-O. Ryan-O literally was knocked out of the game with the first five coconuts that were placed, and he took his one shot at Christa, who we now know he personally dislikes pretty intensely. Not having the Burton/Lill/Darrah/Tijuana thing firmed up, he wouldn't know he had the votes against Rupert, so he wouldn't do it, either. Christa and Sandra appear to have retreated to their position of knocking out Ryan-O and then moving on to Rupert and Burton later, whether before or after knocking out Lill, Tijuana, and Darrah. Burton and Lill, I think, played this to give away as little as possible about their intent. They played just to avoid pissing anybody off, playing at coconutting each other and irrelevant people like Tijuana who didn't need immunity this week anyway. That suggested to me that they're still plotting, but not ready yet to move against Rupert. I just think the Darrah/Tijuana group hadn't hooked up with the Burton/Lill/Jon thing yet, so they didn't know for sure they had the votes. Having already seen one person go after Rupert and lose, they figure they might as well wait another week, considering that Ryan-O is a politically risk-free boot with which to go along. Furthermore, Rupert has absolutely no idea that any of this is happening, so it's pretty clear that there's not much chance that he's going to find out and come after them if they wait until the next tribal council. I think they just decided that there was little risk in waiting three more days until the whole deal was nailed down.