Why? We expect people who drive cars to understand the basics of driving to the extent it is safe for them to drive. Simple diversification isn't a hard concept. Neither is risk/reward in determining where to put your money.
>The aspect of pensions, to me, that satisfies the primary moral constraint of the situation is that you are guaranteed income of a certain level, so that the organization granting the pension has to bear the risk of volatility in whatever funding instruments are used to back it.
But you aren't guaranteed it because things can happen. Immoral or even illegal things, or just having a run of bad luck. Regardless of the cause, there is a risk for the money not being there when you need it, a risk that seems to be worse than a 401(k) or equivalent. That risk includes governments not doing what you think they should've done, because no matter how much you think they should've done something they didn't do, it still wasn't done (in this case, companies weren't forced to fund and protect their pensions).
If you have your own money, you can at least protect against this by having diversified investments, and if you are an adult who is allowed to vote then you can understand the concept of not putting all your eggs in one basket.