You'll need to back up the claim that "only a few very elderly/unlucky die"

What % of people actually survive after being on a ventilator? Because I've seen various studies and anecdotes of this for C19 specifically, with results ranging from "basically no-one" to "80%, at least temporarily, but hardly anyone is actually out of hospital yet so maybe they're going to die later".

Beyond C19, this study suggests roughly something like 50% long-term survival IIUC: https://www.ncbi.nlm.nih.gov/pubmed/26003390

Ventilators are invasive things that themselves can do lung damage. Fairly common for people to choose not to go on them in end-of-life directives.