You may be overestimating the subjective importance of elderly care/life span maximization. I think many would be just as fine with assisted suicide in that set

You may be overestimating the subjective importance of elderly care/life span maximization. I think many would be just as fine with assisted suicide in that setting. I, for one, would rather not end up as a demented mummy which I've seen plenty enough of. Sure there's pre-terminal scenarios where adult children may be of help, but different living arrangements could mitigate that. IIRC I've read that even pre-modern cities have often suffered from below replacement fertility, propped up by countryside migration. Children are decent laborers for subsistence farmers. But yeah, as others have pointed out, it may well be a socially contagious mood that's causing the current trend. Personally, I'd like to think it's having to do with our imposing technosphere causing wildlife extinction, global warming, etc and a desire for better balance, but that may be too optimistic.