I think Michael has realised that the other housemates' ostracising Estelle, and her surviving it has made her popular with Australia, and hence why she consistently evades eviction week after week. Recognising her as a threat to win, he is attempting to diminish her underdog status, by being seemingly inexplicably kind to Estelle, thus hoping to reduce her appeal to the audience.
Been a while since I've watched an eviction show, but I saw tonight’s. I was stunned at how blatant Ben made his hope for Estelle to be evicted when Sonia crossed to them, and Estelle being unfazed by this. Is this a regular occurrence, or was Ben being particularly vile tonight?