Or perhaps these authors could not imagine what being 100+ years of healthspan person would actually be like.

Imagine a civilization where death from biological aging would've happened at the age of 12. Would authors from such civilization be able to predict how a 45 year old would function? Or just extrapolate their (maximum 12) years old experience and come to the conclusion that being past 40 is so psychologically damaging that it would've been better to keep things the default way?

Note that I have just used my imagination, and came to different conclusions, so we are on the equal terms with said authors.