I don't really know how to break this to you, but the economy is really larger than just the US. And the olds transition their spending to health care, prescriptions, and medical devices - and none of that is inexpensive. My Mom is a nursing home and her monthly consumption/spending is higher than it ever was before she didn't know which of her sons I am; and she is one of the lucky ones who can afford it (for now anyway).
Globally there are more people worried about food and water to feed their family next month then there waiting to buy the new iPhone 27 or the Samsung 52.
Maybe I am like a climate change denier (and I think they are f'ng idiots), but I think the population decline proponents have their own agenda that they are pushing. I have thought for many years that one of the primary causes of human influence on climate change is that the planet struggles to heat, feed, cloth and house 8+ billion. Maybe I am the stooge here, if so just call me Kyrie, and watch me walk off the edge of the planet.