https://www.tamu.edu/faculty/payne/PA/Longenecker%20et%20al....
Politics being "My appraisal is more to achieve an outcome in the self-interest of the person reviewing me, than it is to accurately assess my performance."
It would seem that the Performance Review is less a measurement to be taken accurately, and more a Tool to be used to subtly move people.
The study you cited provides a useful enumeration of why. And if you read carefully you can begin to see that the perception of the tool is likely to be incorrect. (that of a measurement to be taken accurately).
To quote the end of the study: " The goal then is not to arbitrarily and ruthlessly try to eliminate politics but, instead, to effectively manage the role politics plays in employee appraisal."