Those entrenched in power and business incessantly whine about "fertility" because they think their capitalist edifice requires constant growth to operate, and constant growth requires a constant increase in both workers (at least until they replace us all with robots or ChatGPT) and customers, or a the most basic level a steadily increasing supply of people from which to extract wealth via some means.

Since apparently nobody can be content to just make a consistent but flat -- and more importantly, sustainable -- profit forever, this necessitates a continually increasing population until we eventually find what the real limit of the planet's human population actually is and the whole thing collapses. No one in a position to do anything about it is willing to hit the brakes now because the majority of them have deluded themselves into believing that it'll either never happen, or if it does they won't be alive to be left holding the bag at the time. This constant trumpeting of braindead "fertility crisis" propaganda is a transparent attempt to delude the rest of us into thinking we need to contribute to keep the meat grinder going.

The collapse of humanity, or at least human civilization, will probably not be instigated by there being too few people. People are great at making more people. We've been finding creative ways to do it for a very long time, and despite everything the global population is still increasing at this very moment. Rather, it'll be instigated by there being too many people to sustainably support.