I bet Salami slicing[1] explains part of it. Before publish or perish culture, It was more common to see more complete papers, that gave a holistic view of the subject, easier to understand and appreciate. Now those papers are sliced into N least publishable units, less interesting and harder to get the big picture in isolation, but hey, why to have one paper when you can have five?

[1]. https://en.m.wikipedia.org/wiki/Salami_slicing_tactics