Seems as stupid as not including food and energy in the inflation number.
I’m going to guess, that the reason why it is not counted, is the limited ability to access the funds. So, yes, the money can’t be used as savings for near term emergencies/needs/desires, but it certainly goes a long way to fund retirement? Since most Americans will live longer as retirees, than as productive workers, it seems only logical that Americans do save a significant amount of discretionary income for this cause. Also, the tax advantages and corporate matches make the decision pretty easy too.
A large 401k balance, also creates consumer confidence. Obviously if you feel financially secure for retirement, then the idea of spending some money on luxury items, entertainment seems normal.
The third traditional reason to save was for a big purchase, but today we just put it on a credit card.