So what's up with "death gives meaning to life"? It seems like a significant obstacle in some of my conversations about cryonics, to getting people to "actually evaluate" (according to me) the likely costs and benefits based on reasoning about the world (rather than e.g. just doing what others do).

Hypothesis: it's a way of coping with fear of death (of one's self, and of loved ones), by convincing one's self (unepistemically) that it wouldn't actually be good to avoid death.
Hypothesis: it's a distraction from what is, roughly speaking, suicidality stemming from a sense that life is hopeless / intractable / only suffering.
Hypothesis: it's an excuse to not be continually burdened by elders.
Hypothesis: it's a way of saving face; it's "just something people say in this situation" to make it widely acknowledged that they didn't act improperly.
Hypothesis: it's a literal belief. If you take someone's food away, they'll appreciate more when they have food; likewise with life. Fear of death pushes you to greater heights. (There's two different things here, really. There's fear of death; the constant threat of death, which you are forced to continually contend with. And then there's actual finiteness--everyone dies before age 100.)
Hypothesis: it's a psyop to get people to not criticize Yahweh for allowing pointless death.
Hypothesis: it's a garbled form of a judgement that, given that we're too technologically far away from preventing involuntary death, we should focus on making the world better for the future while we're naturally healthy, at the expense of long-shots of life extension.
Hypothesis: it's a garbled form of saying that you like knowing the rough arc of people's lives, because it creates a social legibility + shared concepts + social fabric (e.g. rituals of birth, marriage, death), and the current arc involves death around age 80-100.