Why do you think the mandala plays such a starring role in Buddhist art?

The mandala emits positive energies to the surrounding environment and to people that look at it. It is the symbol of meditation, which is a big part of Buddhism. The mandalas contain deities, and the monks meditate with the mandala by asking the deities for healing blessings. Also, when the mandala is destroyed afterwards, that represents the impermanence of life.