I think that's just the mindset these people are led / curated to believe. I've always wanted children, but only wanted two, hard stop. My reason was that while it's good for them to have a sibling to help and support one another with the difficulties of life, it's too expensive to raise children, that they require a lot of money, which I don't have.

My wife, on the other hand, had always wanted 3 children and had been trying to convince me for years; even after we had our first two children back to back (separated by 15 months apart). It clicked for me when one day I realized I don't really need much money to raise a child. That the current financial shape I'm in can't be worse than my father's, who left China with only $100USD in his possession, settled on a foreign land where he don't speak the language, worked and earned everything with his own two hands, with no help at all. Now he is retired with 2 sons, owns his own house with no mortgage and living a modestly comfortable life. I certainly can't be in worse shape financially compared to my grandfather, a farmer, who lived through Chinese civil war, World War 2, communist Mao induced famine and chaos, and he still had 1 daughter and 5 sons. All his children grew up to have their own children and grandchildren.

It all depends on the lifestyle you choose to have, what kinds of tradeoffs you are willing to make, and how you want to raise your children. When I realized that it's alright to raise them cheap, raise them hungry wanting for more, my wife and I did quick work and had our third child. Took me a few years to come to that realization though, so our youngest is 6 years younger than our second.

To say that people can't afford children these days because of financial reasons doesn't make sense to me. We are living more comfortably than ever. I think people simply choose not to have children because they are not willing to make the required tradeoffs (provided that they have a partner to have the children with and are both able to have children).