It's tradition. Japan is a culture steeped in tradition.
It's also misogyny. Keeping women out of the decision making processes means you're going to miss ensuring that you're putting things in place for women, and thus families, to thrive.
The more patriarchal a culture is, the less men think about or even notice the needs of women.
Economics also plays a role. When marriages are delayed, it's because economic conditions have degraded to the point where it's too risky to get married based on hope and a prayer. You lose that blind faith that things will work out well. Being young doesn't mean you're stupid. But older people tend to think that conditions are the same as they were when they were young, so they fail to address needs.
I tend to think a lot of this talk is conflated myself. For example, Japan held itself together as a country with a much smaller population than 60 million in the past. Things aren't the same, but that's still kind of a weird number to throw out there as the point of losing border integrity.
We're all facing environmental collapse, one of the single best things we can do is to draw down our populations mindfully and purposefully rather than by chaos and starvation.
Populations could be stabilized by immigration. Euthanasia could be made available and acceptable to anyone over 50 or 60. We're all going to die. It's weird to me that shame is heaped at women for not having children under perilous circumstances in order for old people to have someone to care for them. Again and again, that's the argument. But there's never any discussion about how medical advancements have extended lifetimes. What about the shame of taking up resources, demanding an otherwise able bodied younger person who could be wirking to stabilize the environment to care for you through old age while your life is being extended and after a lifetime of poor habits that led you to needing such extensive care in the first place? Why can't we have that discussion?
(Granted, that's more directed at my own country, US, than Japan who comparatively lead much healthier lives.)
Frankly, IMHO, Elon Musk needs to shut his yap about this. He doesn't want to lose his cash cow and the chance for Mars, which is delusional anyway. All that money he and the other billionaires have. They could do something. What's stopping them from giving grants or opening child care centers if they care about a population crisis so much?
Not a damned thing.
Sure are quick to shame women though. Couldn't wait to jump on that boat.
My daughter, the Urchling, also pointed out that that perde tage of unmarrieds is conflated to look like more of a problem. Half of all people includes the formerly married who have lost a spouse, children (non adults), who will make up maybe 20% of stable population, young adults who are still in the process of achieving their education, and are dating, people who are looking to marry but need to save money to privide for a family or get a start in life, people who are delaying settinf out their own family and life due to taking care of bieth family obligations, etc. Her point: exactly how many of that "50%" are actually off the dating and family market and at what point is it truly a problem for population stability? What are the other factors being connivingly concealed here?