Why do some articles recite/repeat known concepts?
Not everyone who reads a paper is going to be in your field and have the same background no matter how basic it might initially seem. In researching literature, I often come across sociology, economics, history, etc, papers. That initial regurgitation in a paper might seem really obvious to sociologists, economists, and historians, but it isn't necessarily so obvious for me (and nicely tends to give references if I feel the need for further background knowledge).

It also helps out people in the field, especially when they're not as current on the specific topic (when was the last time a scholar of modern American theater read Beowulf? Likely graduate school). It helps for understanding the approach used as well as seeing the paper's context, relevance, and importance within the field. Even at a basic level, when someone recaps a plot/situation in a single paragraph for me, it's enough to jog my memory and save me from needing to pull the book back out and read a hundred pages just to follow the paper.