Pancreatitis in cats may be caused by several factors.  Here are some to consider: 

1)  Inflammatory Bowel Disease - It is thought that bacteria migrate into the pancreas, triggering an infection which leads to inflammation.
2)  Trauma - When I interned at the Animal Medical Center in New York City, I saw several cats develop pancreatitis after falling out of their high-rise apartment windows.  Now I see it develop occasionally after cats are hit by a car.
3)  Toxin exposure, especially organophosphates used in the garden as insecticides. 
4)  Other reported causes that I have yet to observe - Feline distemper, toxoplasmosis and drug induced although this seems to occur more frequently in dogs on azathioprine.  

The really frustrating thing about pancreatitis is that I often never find a definitive cause.  I personally think it is most often related to diet, especially the long-term use of high carbohydrate, grain based diets.  Hopefully research will provide answers soon.