"Post Partum Depression" exists due to the isolation of the nuclear family. It's the dread of the realisation that your whole life is permanently tied to your kid from now on, with no recognition of it.
Back in the day you had a large support network, grandparents, parents, aunts, cousins, etc and having a child was inherently a social event, it wasn't solely the responsibility of the mother. In such an environment the dread doesn't even occur. You got social status, support, admiration, recogniton and help from your entire family through your child. That's how it became fulfilling. Everyone around you found your baby cute and charming, gave you gifts, helped with taking care of it and so on.
Today? You're making tiktok videos as a cry for help because your friends don't care, your parents are too old, you barely know your cousins and your partner is busy working and you can't even afford the Latina nanny. It's genuinely so much more isolating. No wonder birth rates are falling.