Can someone enlighten me how did he end up prediction extinction by 2300? I see words, but it makes no sense to me. Even if it correctly peaks at 2065, even if

Can someone enlighten me how did he end up prediction extinction by 2300? I see words, but it makes no sense to me. Even if it correctly peaks at 2065, even if it declines, it should stop at a stable level since most developed nations usually have 1-2 child per family today. I cannot imagine the next generations doing nothing with a laid back attitude and slowly let us die out because nobody wants to make babies :)