> spending money or participating in that procedure would be entirely irrational from their perspective.
Roughly as irrational as having children. Humans are not rational beings.
> What could they ever gain from that?
Continuation of what they were trying to achieve in life.
> Spending the same resources to prolong your existence (even in a suboptimal state) seems literally infinite times more rational.
That entirely depends on what you value. You may value living in your suboptimal state less than chance at making something happen that you wanted to see happen but due to bodily limitations are no loger able to progress on.
Roughly as irrational as having children. Humans are not rational beings.
> What could they ever gain from that?
Continuation of what they were trying to achieve in life.
> Spending the same resources to prolong your existence (even in a suboptimal state) seems literally infinite times more rational.
That entirely depends on what you value. You may value living in your suboptimal state less than chance at making something happen that you wanted to see happen but due to bodily limitations are no loger able to progress on.