What impact do you foresee any economic gains from childlessness having in 100 years, if your advice is followed universally? Who will inherit those gains?
I believe the context for the advice is directed to whoever is capable of having children. So, economic gains are meaningless to them when they're dead in 100 years.
Put another way: let's say everyone who is capable of children follows your advice. To whom are these economic gains meaningful in 100 years? Who would their parents be?
What you're implying is meaningless to the ones that are dead. So maybe you can now realize why I wrote my response and it was directed towards anyone considering conceiving a child.
OK, from a pure hedonistic view - let's say at some time in the future, there are no more humans left. Why would it make sense to invest anything into economic gain in the time before that happens? You'd rather run the economy into the ground to extract as much value as you could from it, before the end of human existence. You - or else someone else who is the last human alive - are "leaving something on the table", so to speak. Otherwise they are just leaving value around for wildlife.
In other words there would be a time, maybe dependent on the rate at which remaining humans can unwind the human economy, past which any effort at collective economic gain wouldn't be worth it.
I think of this as a non-issue; either my partner, or a friend, or a charity of choice will inherit my gains if I don't spend them all enjoying life first.