Why does enemies attacked Oyo Empire but Couldnt attacked Ilé-Ifè?

Both Oyo Empire and Ile-Ife are from the same ancestors, they are brothers, they are One, they are children of Oduduwa. According to existence, Ile-Ife Kingdom existed before Oyo Kingdom.

One of the son of Oduduwa migrated from Ile-Ife to create Oyo Empire. All sons of Oduduwa adopted a name called Yoruba.This is just like forming an association. i.e. like saying "Association of Oduduwa Children". Since they're all a Traditionalist, they usually consult their ancestors and ask questions before doing anything either it will be good or harm them. So they consulted their ancestors if the name Yoruba will be good for their association. This is how they are called "Yoruba Omo Oduduwa"

Oyo empire existed between 12th century to 18th century. During its apogee (1650–1750), most of the states between the Volta River in the west and the Niger River in the east. It was the most important and authoritative of all the early Yoruba principalities.

The visitors from Mali who came for business in Oyo Empire brought them a religion called Islam (Esin Imale) in peace, and some of them started embracing the religion since it was brought to them peacefully. There was no fight, no war.

As at this time, Ile-Ife under the control of Oranmiyan whose stool title is called "Ooni of Ife" never gave a room for any foreign religion, and they only worships their ancestors. The rulers of Ile-Ife told the Oyo rulers to caution his citizens from embracing another belief that is different from their ancestors belief, but it seems it couldnt stop until the religion started spreading as they practices the religion and also worships their ancestors.

Those who practices this new religion among them were the first to receive some particular visitors called fulani. The belief and mentality of oyo people about islam was entirely different from the way their newly welcomed visitors practices it.

Those newly welcomed visitors were later the ones that launched a sudden attack on Oyo Empire after they have penetrated deeply through the alliance of some Oyo Citizens who practices same belief with them. It was later believed that no one was aware of these visitors attacked.

The fleeing Oyo citizens later regrouped and prepared his armeies who are mostly Traditionalist (ancestoral worshippers). Oyo armies retaliated and got back the control of their Territories.

When Ile-Ife heard of the sudden attack on Oyo Empire by the visitors, the ruler of Ile-Ife sent both physical and spiritual chariots to support Oyo. It was a victory for Oyo Citizens after they fought back and get back their land.

This is where a popular saying comes out "Isese Ni Agba", meaning "ancestral is the supremacy"