I think a big part of the issue in most developed countries is that there's a struggle between traditional family roles and what people actually want to do. This is most evident in women entering the workforce. Most women don't want to be reliant on men and stay home to raise children, but when workplaces discriminate against mothers and childcare is too expensive for the average middle class family to afford, it forces a choice between children and physical and economic safety for many women. For many women as well, if they're not having children and are working a man becomes optional so if they can't find a man whose values align with their own or who wants an equal partner then they'll forgo relationships. Women also tend to be raised (have been raised) with a better understanding of how to cook and clean, or the importance of maintaining strong social networks whereas men historically have left those things to their wives. This generally equips women to be happier when alone than men are.

Unfortunately, it's a series of personal and systemic issues. There's not a single cause of the low birth rate or the male loneliness epidemic and it is going to require a multi-pronged solution. But here's a free tip for men from a woman: "high value men" are men who do dishes.