Interesting that the Hobbit is only one, regular length, book (300 pages?)... that was made into three full length movies.
Yes, Jackson and Co. made 3 movies from one book. It’s not so hard to understand when you can interpret the heavenly music of the Ainur. That holy music makes this sound, “Cha-Ching!” It worshiped amongst the lower men of Hollywood.
Jackson added a lot of material from the Appendices of the LotR books. Tolkein had put a lot of the back story and connecting stories (relating the events of “The Hobbit” to the plot of “The Lord of the Rings”)into the appendix.