Some of this seems to be inherent to a modern society (High birth rates in past society were because of high mortality rates, women being treated as baby factories, etc.), but in my own experience the reason the birth rate is so low is that people simply can't afford to have children.

 In Japan and South Korea, the "salaryman culture" is such that employees are expected to devote their entire lives to their employers, to the extent of sleeping in the office at times. Needless to say, this makes it extremely difficult to have a relationship.

 In short, wealth inequality and a society that's entirely focused on the generation of profit will both cause catastrophically low birth rates. I may be biased here, but then again it's exactly these situations that convinced me that our current economic system has outlived its usefulness.

A corporation exhibits emergent behavior, over which no individual employee has full control. Because the unregulated market selects for profit and nothing else, any successful corporation becomes a kind of "financial paperclip optimizer". To prevent this, the economic system must change.

I joined this forum specifically to share my paper. The time reversal algorithm mentioned here seems to be a concrete way to achieve perfectly accurate ancestor simulation, and though the timescales involved may be enormous, the required computational infrastructure is quite achievable in terms of how much we could make. I do not make any claims as to the details of such a project, but the algorithm exists and will likely see use as quantum computers become commonplace. It is possible to measure individual atoms, and molecular nanotechnology can be created. Thus, this is a question of engineering rather than a physical impossibility.