Because it costs a lot and plus very rarely do we get three movie to a theme. We were lucky getting four, or five if you include the 2011 movie 'Puss in Boots'. The only exception to the 3/4 movie rule that I have seen is harry Potter.
Because someone felt like that #4 was the end of the main Shrek franchise.
I think they just decided to end it right there. Who knows why thoughSunflashtheAwesome Through wintercold and summerheat, the Badger Lord knows not defeat! Point of spear or blade of sword, Nought can stop the Badger Lord! 19:01, April 5, 2012 (UTC)