Exactly. And the cause is the mutually reinforced effect of capitalist consumerism and feminism.
One of the causes why people postpone having children is financial insecurity. In their mid-twenties they cannot afford to have a home, they are unable to secure the costs of first few years of raising child, when they don't know if they will have a job in three months and they have zero savings. Add student loans to the mix, popular desires to travel the world, to "live" and it's obvious why the developed countries have problems with natality.
One of the reason of population boom in Czechoslovakia in 1970's was the policy of support of young families. Newly wed pairs were were provided security, they got their own homes, they had job security[1], they got financial support for raising children. It wasn't a luxury, you couldn't lead a lavish life, but you knew that if you have a child, everything will be OK.
[1] we are abstracting from the fact, that in socialist countries it was unlawful to be jobless. You were provided a job, but it didn't have to be a one you would like.
Otherwise, thank you for the explanation and I do apologize for my ignorance.
(Also, I'm still confused about the feminism thing)
Because with immigration, you didn't solve the underlying cause of why people don't have kids. You just muddled the observable status for a while.