A very good theory. You aren't nearly as brainless as you first appear to be. [High praise???] Indeed - it was clever of the staff to only vote once, as that was all it would take to finish Diva. But, if there was no communication between the staff during the trial, wouldn't we assume all of the staff would undertake the same calculus? Each individual would likely vote for Diva to ensure someone voted for her.

That is, unless: they were communicating during the trial; they had agreed beforehand that if the group would abstain, only one would vote; or they didn't know the votes would be anonymous and one decided to sacrifice themselves.