That's because performance is easily gamed. A manager could make someones performance look bad, or good regardless of reality. That's why you can suddenly be a good performer or bad performer just by changing companies. It doesn't even have to be a conscious thing. Everybody is subconsciously biased.

If you like don't like someone, you performance managament them out by like giving them lots of terrible tasks or stupidly high targets. This is a well known technique, recommend by most HR people.

Anyone who's been work for a decent amount of time, knows this. Workplaces can be more like high school playground the with popular kids and the outcasts, then a merit based thing.