There are two reasons you might not want all retirement savings money to be wholly in control of the saver:
1) Some folks are simply really bad at saving, which ends up being rough for others around them and for society, not only affecting them. This reason tends to rub some folks the wrong way on principle, so they may prefer to disregard it, but it is true as far as it goes (principle aside) [edit: I mean doing anything about this for this reason rubs some folks the wrong way, not that they disagree it’s a real phenomenon]
2) Money directly available to people is freed up for rivalrous zero-sum spending. Think: bidding up scarce resources for your kids, like good schools (which can mean housing). In a world where 100% of comp is employee-directed, this punishes responsible savers.