Relative sizing aside, the 401k may not be the largest asset, but it IS the asset that they can use for liquidity when they get old. They can't just sell their house, nor is a new or second mortgage a good idea.
It is entirely legitimate to not want to wipe out the savings of the middle class just so you can get at the rich people. The rich people may lose a bigger absolute number, but the middle class will lose out proportionately.
I know what you're saying. I would have lost quite a bit of value in my portfolio had what I advocated transpired. But you know what happens when people are shielded from the consequences of their actions? They do it again.
It's not about getting at rich people. It's about exposing the criminality that lead to the crash. There was massive fraud at all levels; from the banks to the loan originators to the ratings agencies. But because of the way it was handled, most people don't know that. The banks that were systemic risks, too big to fail, are today even bigger.
We haven't corrected the conditions that allowed the crisis. The people who caused it through fraud and negligence have not been held to account. And the public doesn't understand what really happened and why. All that is by design, of course. But it also guarantees that it will happen again. Sure, handling the aftermath of the crisis the right way would have been painful. But many people were hurt by these bad actors, and have had no restitution. They lost their homes, declared bankruptcy, etc. Hell, people were foreclosed upon who didn't even have a mortgage! None of that was dealt with, and the people who made it happen got 7 figure bonuses. Corruption has consequences, and so does not dealing with that corruption.