The old pension plans will pay retirees for as long as they live.

The 401Ks are a finite amount of money that needs to be metered out over a period of time and will run out if miscalculated.

So.... how long are you planning on living?

If you save $500K and you allot yourself $50K/year
you have money for 10 years (give or take what you get in interest or return on your investment). Retire at 60-65 and you run out at 70-75 years of age. If you're still living - too bad.

Now, compound the problem:
Some people are greedy. They are the people who have maxed out their credit cards and then claim bankrupcy, dump the debt and start over again. These people will take $75K/year and live the good life for 7 years and then tell the government thay are out of money and ask what the government is going to do for them. These are the entitlement people. And we know that our government is going to say, "My gosh, we can't just let them starve to death. What are we going to do?"

This is the problem nobody has started to think about yet.