I was reading this article this morning for whatever reason this popped in my head. Population decline in another potential reason for The Fermi Paradox.

https://www.derekthompson.org/p/why-the-whole-world-stopped-having

My theory is as alien societies going through the same thing we are going through lose the momentum needed to develop the faster than light technologies needed to reach beyond their solar systems. As the population ages, the economic reality of funding the medical care needed for an aging population doesn’t allow for, as many think, frivolous spending on space travel.

The number of civilizations who find a workaround to this, and to reach out to the stars, are fewer and fewer, which reduces the likelihood of a chance encounter.

I’ve been interested in demographics for the last 20 or 25 years when my kids started to creep up on the age when they would have children.

As the population ages, the economic reality of funding the medical care needed for an aging population doesn’t allow for, as many think, frivolous spending on space travel.

 I disagree.  I think elites will let billions die of old age and go to space anyway.