Saints was just a way to appeal to polytheists back when everyone hadnt moved on from multiple gods.
That fertility goddess? She was a person, and now she's a saint and a road to jeebus. Some chief whose corpse you've been carrying around for 100 years? Perfectly cool, lots of Christian churches did the same thing.
Especially for Catholics, praying to a saint is like calling God's secretary, that's why they all have their own fields like "gaming".
Locals got a way to continue existing rites and festivals, the local leader got to tell the church they were converted, and no invasion "had" to happen.
It was the franchizification of millennia old religions that are practically extinct today.