Why did the author do this? Why make the book more complex and sometimes frustrating for the reader?
This is a really interesting point. I agree with you saying that it makes the plot more interesting because it goes deeper with the characters with all of their connected lines. And at times, it's confusing, like when Gwendolyn just shows up out of nowhere or (spoiler) when Meredith randomly has a sister on Grey's Anatomy. All those lines are connected for a better experience for the reader or viewer because it's not just some basic, straight forward book. or TV show. Instead, it's a complicated, suspenseful story where the reader and viewer don't really know what's coming next. I do agree that this is probably one of the main reasons the author does this but maybe another one is to create many different interpretations or understandings of the same story.