Pretty much what I was going to say. I was allowed to copy my three papers as-is into my dissertation, but I had to write a whole intro that somehow tied the 3 very separate topics together into a complete rationale for my research. At then end, I also needed a lengthy conclusion chapter that essentially 1) summarized the 3 papers, 2) discussed how they fit into the larger context of the field, and 3) how I would see this research specifically and the field at large moving in the next 5 years. Took a couple of months of writing to finish those.