I assume you mean low cost broad market index funds when you write 401k, but what other mechanism has offered financial security to so many other than having lots of productive and well networked kids that believe in helping you when you are old?
There is, of course, taxpayer funded retirement benefits, but that is just taking from others’ kids.
The pensions that are so underfunded (either due to corruption or bad math) they need repeated bailouts from federal taxpayers? Hope you’re in a sufficiently politically influential union.
If federal taxpayers are going to bail out old people, might as well be the whole stock market so it’s not just a few politically influential unions that get bailed out.
Union members not in an insufficiently influential union can have their benefits cut:
What do you think pension funds invest in if not the same things as my 401K?
Pensions are useful to individuals, because they support you until you die (while your 401K will either run out before you die, or will 'waste' money in the bank if you die before it runs out). But they aren't a magic money tree. They are the exact same formula. Money in, money out, it just gets distributed a little better.
There is, of course, taxpayer funded retirement benefits, but that is just taking from others’ kids.