> part of the journals' service is helping academia determine who the best scientists are
Could you elaborate? If you're referring to the revered and important process of peer review, isn't that explicitly and exclusively performed by other scientists, paid mostly in public funding?
The idea is that a good publishing record gives one better career prospects. By accepting and rejecting papers journals are giving a signal used by academia in their hiring and promotion decisions.
If you're an administrator overseeing a scientific department your skills are probably in administration, not chemistry or physics or what have you. What you would really like is for a team of top chemists to tell you who the best chemists among your staff or hiring prospects are. That level of consulting would be cost prohibitive but the journals are providing a similar service that is apparently being exchanged for exclusive publishing rights.