When scientific journals began to offer full online access to their articles in addition to the traditional printed volumes, scientists gained access to more journals and easier access to back issues.
Given that ...
Once science journals started offering all their articles online (in addition to in print), scientists gained access to more journals and easier access to back issues.
Why is it that ...
This didn't lead to a broader variety of articles being cited; it led to a greater tendency among scientists to cite the same articles as each other?
Evaluate / Goal
We would think that if you have access to more journals and to back issues, you'd be exposed to a greater variety of articles and so there'd be a greater variety of citations.
We need an answer to explain why we're getting greater repetition of citations. It should be something attached to the new reality of being able to search online or something that changed contemporaneously (i.e. at the same time these journals started offering their stuff online, something else also changed that led to greater similarity of citations).