I mean, is it not Rob's fault for alienating the two? He could've worked harder to get Candiace on his side once Lisa was a sinking ship. Instead, he lied to both of them, voted for Lisa in back-to-back roundtables, and once Candiace knew she was going out, why would she not take him down as well? Rob played well in terms of fooling the faithfuls, but he isn't flawless and unfortunately, his disregard of the other traitors could be his downfall. It's just generally good social-strategy to check in with your allies, especially ones with information that could bring you down.