I don't understand why people think they know why stocks move up or down. There are clear cases from time to time, but in general the market doesn't explain itself. The reasons may not even be explainable in a way that's comprehensive to a human.
Reminds me of this question - why did the USSR collapse? You can describe dozens of influences which acted all at the same time, but there isn't a one paragraph summary answer.
Humans seek to understand phenomena and they use narratives to accomplish that. Accepting that there are multiple factors always involved and chaos reigns is disturbing.
Then please explain why birth rates throughout human history, when life was vastly more difficult and dangerous than it is now, were so much higher?
Nobody had to meet this bar you set before. Let's just be honest here. There were three recent developments, all of which were, by themselves, good things. But those three things, combined, created an unprecedented phenomenon.
The 3 things:
1.) The birth control pill decoupling sex from pregnancy. 2.) Women being granted autonomy and being allowed to join the workforce and leave marriages without suffering economic and social destruction 3.) Social support programs to create a poverty safety net funded by taxpayers instead of charity
No society on the planet ever had these things until the mid to late 20th century. And these things all contribute to radically reduced birth rates, in every single society that has implemented them together.
This take of "all you have to do is make the society encourage family formation" makes it sound like the three developments I listed are irrelevant, and that humans always just had this explicit menu of options that made family formation an optional pursuit, independent of a good life. That is simply not the case.
We need to be honest with ourselves about the uncharted territory we're in. It's not simple. Modern humans live in what would have been historically viewed as a Utopia. Our ancestors 5 generations back would have viewed our "jobs" as fake. They wouldn't even recognize what we do on a daily basis to earn food and shelter as labor of any kind. We have entire metropolises filled with people with soft hands who have literally never had to participate in their own survival from the perspective of harvesting food or cooking/heating fuel. Your comment just reeks of someone who is disconnected from the historical realities of 99.99999% of the humans who have ever lived.