Why do we adult persist in lying to our children. I told my kids when they were very young. Daddy? when will father christmas be coming to leave the presents

Why do we adult persist in lying to our children. I told my kids when they were very young. Daddy? when will father christmas be coming to leave the presents under the tree? My reply. He wont, its your mother and I who buy presents for you because we love you. When you go to sleep I will put your presents under the tree.