"Low" is a relative term, and so we must ask "low compared to what?"
That isn’t going to work.
More importantly, once you're in your 80s it's probably safe to start whittling away at that principle.
You can get, averaged over several years, something like $50k/year from that.
I don’t think it’s sound advice to keep your retirement in stocks when you’re actually in retirement...
But you also don't know how long you'll live for, so to have your money doing nothing for 20/(30?!) years could hurt. My wife's grandmother is 99. That's a long time in low-growth near-cash.
Your point about $20k not being much is true, but I also would presume that someone who's saved that much probably would have some social security coming in, at least doubling that.