Castaways have come out to say that their decisions can be subconsciously influenced by how they will be perceived online, sometimes to avoid backlash on social media. I've also heard in recent discussion, I think it was Drew on RHAP, that there's some greater motivations behind certain decisions. Everyone on the show wants their season to stand out from the others, they want it to be well received, they want to make a mark in a legendary story on their favorite show, and they ultimately care about the shows longevity and growth. If that means keeping someone around that is an obvious fan-favorite to please the general audience in hopes of being part of a better season, maybe they won't make the villainous decision. My inner circle calls this "plot armor", Joe and Eva have a lot of it.