Why do carnivores like tigers have smaller short intestine ?

Herbivores have long intestine and carnivores have shorter intestine.

The length of small intestine depends on the eating habits of an organism. Food habits of herbivores are generally plants and trees, which are full of cellulose and fibre. If an organism is herbivore for example cow, its chief food component would be plants which contain cellulose. Cellulose is large and complex substance, its digestion process is quite longer whereas in case of flesh eating animals like tiger, the digestion takes place easily and faster as meat is easy to digest. So carnivores have smaller intestine than the herbivores.