Stack ranking is based on whatever metrics team leaders/supervisors want to use. It often becomes a simple popularity contest, and leads to an 'every person for themselves' culture which can stifle innovation and collaboration. Even in cases where there's a quantitative metric used for ranking, it's often subject to gaming, such as the use of number of commits or ticket closures.

Also, stack ranking doesn't account for any flaws in the systems of the company itself - if you have poor processes that hinder productivity, it's going to artificially diminish the rankings of employees that have to use or are subject to those processes.

There's a reason why companies that use it tend to have much higher turnover than companies that don't - because it makes for a really unpleasant workplace.