"someone thought surrogacy might be purely a recent phenomenon"
Surrogacy as we know it - namely, gestational surrogacy - is a recent phenomenon.
The thing which is apparently called "traditional surrogacy" I wouldn't call surrogacy at all, it seems more like enforced adoption or slavery to me. A real life Handmaid's Tale.
I cannot imagine why a woman would willingly and intentionally conceive, birth and give away a child which is biologically hers in both senses of the word - genetically and because she physically bears the child.
(Unplanned pregnancies resulting in adoption are different.)
I struggle to understand why a woman would be a surrogate at all, but if conceiving with the intention of giving the baby away, it would seem logical to me to use an egg which is not your own, to help you see the baby as "theirs" not "yours".