Why is there chanting during meditation?
Slightly the wrong question… chanting is one kind of meditation. Meditation is not just sitting meditation, and even with sitting meditation, there is usually a breathing discipline along with other disciplines of posture, direction, duration, etc.
Chanting is part of Buddhism.
Buddhism started as an oral tradition (with no written language at the time). Thus, repeating the Teachings orally was one of the ways to pass them from one person to the next.
Currently, every Buddhist sect or school would chant part of the Sutras (words of the Buddha) as part of any religious service.
Gassho (with palms together), Rev. Ron