My father has been falling a lot why is this?

Many possibilities. There are a number of possible explanations, and it's wise to figure this out before he gets seriously injured. Some people fall because they don't see well - easy fix. If he is diabetic, he may have peripheral neuropathy and not feel his feet as clearly as a normal person. He may have balance problems. He may fall due to muscle weakness; has he had a stroke in the past? Go with him to the doctor.