Nowadays everybody is on defined contribution plans. The average 401k balance for retiring Americans today is just $180k, which translates to a meagre $7000 per year in retirement income. Worthless.
Yes $180k doesn't go far. Factor in that a lot of them may have mortgages, car loans, and other debt. At least they also get still social security. In many cases the 401k balance could be much higher if they had taken all of the options they had to contribute. Of course they thought they couldn't to afford to. It never occurred that just maybe they were living beyond their means and couldn't afford not to.
Some plans are much better than others with more generous matching contributions and so on, but often folks don't take full advantage. I worked where the plan was very good and some didn't take advantage and/or took out money for stupid reasons paying huge penalties. Imagine draining your retirement to buy stuff like expensive new vehicles.
The other thing is that some expect too live too high on the hog after they retire and out spend their means.