Training a dog

Question
Why is easy to teach a dog to come when they are call, but difficult to teach them not to chase rabbits?

Answer
Hi,
You didn't tell me the breed so I will answer generally.

Remember, before dogs were domesticated they had to hunt for their food.   Many breeds of dogs are still bred to hun, so when a dog sees a a rabbit, his basic instinct takes over.  One of the hardest things to teach a dog is go against his breeding and his basic instinct.
Nancy
ps  You will have to get a positive or negative reinforcement that is more interesting to the dog or at least breaks his attention on the rabbit.,