Often, if the concept is presented in a more complex way the reason is that the author wants to emphasize and explain how the concept relates in a non-trivial way to some other deep concept; thus you learn a lot more than when the author explains things in the most simple (and shallow) way.
I don’t see how that is beneficial. If a simple concept relates to a complex one then explain the complexity, don’t add it.
IMO the most common reason why something is presented in a more complex way is that it is badly explained.
Of course, most common or not, each case is different.