If you retire. You might die before retirement age. Also, by the time you retire you might be too infirm or sick to even enjoy your retirement. Many people also have such a crappy work/life balance that they don't know what to do with themselves when they retire, so they're miserable even when they retire.
I don't understand the negative use-cases from your statements.
"if you retire"
"if you didn't die"
"you maybe too sick"
Are you suggesting not to invest at all because "YOLO, we'll die, or sick-and-die anyway".
Saving money does not mean you have to live below poverty line. It means you have to "live within your means" => "balance in all things". The hardest thing in life is to deal with "change", in this case, "changing your lifestyle". Those who are not used to "live within their means" will absolutely struggle to do so down the line.
Nobody suggest anyone to put away as much money as possible and live miserably. If we go back to the simplify calculation above given the situation where one cannot afford to travel abroad _right now_, investment can help them with that problem! Nobody say not to touch your investment before you retire. You can withdraw occasionally for reasonable splurge.
Starting Point: $10k
Annual Contrib: $1k (that's $1k per year)
Years to Grow: 20 years (that's $20k contribution)
Annual Rate: 5% (ETF bloggers says 10%, but let's half that)
Total Value: $61,252.23
Money you put in: $30k ($10k + $20k for 20 years)
Money you get: $31,252.23
So let's say at the 21st year, the stock crashed. The crash needs to be more than 50% in order for you to lose your capital money.
First, I believe you can tell your financial institution if you want to cash out.
Second, by the time you retire, usually you don't put your money in high-risk investment but instead if something more "reliable" so the chance you get hit with 50% lost should be at minimum.