I can only think of one.
You’ve already got a kid, so you’ve secured your family name and DNA.
Her child is about the same age and sex as yours, so they can interact and relate with one another and, most importantly, there is no risk of her being violated.
Your frame also naturally infers 100% authority in the relationship.
She isn’t a feminist, and takes ownership for her life, and holds her kids accountable to my standards.
She is, at a minimum, financially equal to me.
She is a complement to my life, and certainly not the focus