Why do Chaoshan use chicken to strike oil and light fire?

Because chickens can "drive away evil spirits".

In our folk beliefs, the origin of rooster to ward off evil spirits still has its significance! It is said that the rooster can pull the sun and has the divinity of exorcism. The crow of the rooster complements the light, so the rooster also plays an important role in red and white, exorcism and divination.

Burning oil and fire is the custom in Chaoshan. When the new house is built, the owner must invite Nishimiya (the mage) to come home once to drive away evil spirits, so that he can live safely with his family.