Because it worked for Harry Potter
(critically AND commercially) and Twilight
(commercially, but not critically because those movies can suck a moose's b-hole for all I care), the final installment of The Hunger Games
will be split into two movies, even though the last book had a little more of a reserved pace and could easily be crammed into one movie. But then they wouldn't be able to double their income, so why bother? TWO ...