There is another paper out on Causes for the Persistence of Impact Factor Mania. From the abstract:
Numerous essays have addressed the misuse of the journal impact factor for judging the value of science, but the practice continues, primarily as a result of the actions of scientists themselves. This seemingly irrational behavior is referred to as “impact factor mania”.
Goodhart’s law: When a measure becomes a target, it ceases to be a good measure.
First Law of Metridynamics: The observed metric will improve.
Even a cursory glance indicates that the impact factor mania is perfectly rational. Given the increasing distance between administrators who decide on grants and promotions and the science they are trying to judge a single number is easy to judge on. Deciding on the actual impact of the science is difficult, time consuming, needs deep knowledge and you are still likely to go wrong. On the other hand, some function of the impact factor, is a single easy to judge number. Even if you know that the number is not particularly accurate, you can still justify an action later on based on a third party number.