Hell if I know. I think it's pretty inappropriate for anyone to exert any kind "pressure" on anyone to procreate. Society can go fuck itself with that bullshit.
I remember the father of a friend telling me that since I was an intelligent woman, involved with an intelligent man, we had a moral obligation to have children.
We didn't, and I never have.
My experience was the opposite. People weighed in on the fact that I was having kids. I expect that it's a case of no matter what you do, some busy bodies feel like they must let you know what they think. Everyone gets pressure. Damned if you do, damned if you don't. They should mind their own damn business
My oldest is not my biological son which surprises anyone who finds out. We are much alike, but I came into his life at 16 months. The next two, come a few years later and although my now ex wife agreed I got a vasectomy which she later complained about. I love my kids, but three is easier than five. Oh, my ex kept me around a lot longer than may have happened. She decided I shouldn't adopt the oldest so she could collect money and then later used my love for him as a wedge - you will never see him again, just his siblings. I put no pressure on my kids and at this point expect no grandchildren. I am perfectly fine with that. Now that I'm divorced I thought about adopting my 37year old. He says save my money, he knows who his real dad is. I am very proud of my kids; Not only do they love each other, they like one another, even taking vacations together.
I have two daughters, ages 49 and 51. One was married for ten years and got divorced. The older one has been married for a few years. Neither of them had children. Neither of them wanted children. I never questioned them about it but told them it was their lives and whatever decisions they made in that regard were theirs. The younger has been living with a man for about 15 years. He has grandchildren and they call my daughter, grandma. I have never been upset that I have no human grandchildren. All my grandchildren have four paws, fur and meow. That's just fine with me. I was pregnant with my first marriage. I wanted two daughters. I got two daughters. I had a miscarriage between them early on. I am very proud of the women they have become and love them so, so much.
I don't hate the idea of China's law of one only. I know there is much more to it, but what in the world is the point of having a handful of kids. Or 10, or more!!! I had a friend in school who was one of 18 kids!!! What the hell. The parents offered no love or support, did not even come to graduation. I say that's bullshit. The world is overpopulated, too many people with too little, no or awful parenting and the circle of dysfunction is never ending.
As a little kid in the 60s I heard talk about the "population bomb," and I realized then that the world did not need me to have kids. Two hundred years ago it was necessary to produce farm hands to work the land and a large percentage could be expected to die young. Nowadays having kids is a luxury, not a necessity. In decades past I got not so much pressure as surprised reactions that I was opting to not have kids. It was as if the default setting on the white, educated, heterosexual, middle class, American male was always procreation. Now, with climate change nipping at our heels and civilization on the brink of agonizing change if not outright collapse, I think people look at my decision not to have kids in a different light. I certainly have no regrets.
Because women are brainwashed to believe that they can't be complete humans without pooping out crotchfruit. It's not going to change until parents start handing their daughters briefcases and calculators instead of Barbies.
The religious brainwashing (Be fruitful AND multiply) is deeply ingrained.
Each generation wants to know that the family tree will continue to thrive, so the parents of young Newly Weds encourage them to have babies.
I say of pregnancies, "If it happens, it happens. If it doesn't happen, that's cool too."
When I was a kid, the 1960 Census counted about 2,000,000,000 (2 Billion) people in the World. Today, the population is getting close to 8,000,000,000 (8 Billion) people. That means that the population has quadrupled sine I was 10 years old. Young people should consider that when deciding if and when to have kids.
I'm childless, so I'm certainly no authority on this. I can only make some guesses. My guess is that there are a few unconscious beliefs that drive the "have the child thing": First is that a child will make you and your parents happy. Second is that having a child will bring true, unconditional love and the Third is that a child will be present and tell you how much they love you when you are dying. (or a way to avoid the fear of dying alone.) These things are sometimes true, sometimes not.
As for societal pressure, I wonder if there is an unconscious belief that there is no other purpose to life than to bring a child into this world. That children are our future and without them there is no future.
It's interesting when the press notes that human population growth rates are going down in some areas, that they always present this trend as "concerning". As if the human species will cease to be if the growth rate declines or flattens out. Does the planet need 7.5 billion people? (rhetorical)