It's a sort of complex but fairly well understood demographic trend globally if you want to look into it. There's not really one clear cause. In general more e

It's a sort of complex but fairly well understood demographic trend globally if you want to look into it. There's not really one clear cause. In general more educated people and professionals have kids later and have fewer of them. Having kids earlier is also a significant barrier to completing education and entering a high income profession so there's an effect there too. This isn't all of it just the two most clear examples.