Why did God put lions on earth?

The is no "why" lions simply "are". Lions evolved from more ancient animal types under environmental pressures. This process is known as evolution. It is a response to environmental pressures where some members of a species will do better than others and enjoy an advantage in successful breeding. Their offspring will have the advantageous genes and carry the successful characteristics and pass them on to their young. Over the years the cumulative effect of successful gene modifications changed some early small carnivore in lions. Similar changes create all of the larger cat-like creatures - tigers, pumas, jaguars etc.