Low taxable incomes doesn't always mean low real income though does it ?
Those who derive a large non taxable income from super are doing very nicely without getting another refund on top of that.
The income being drawn from Super could be capital - from non-concessional contributions paid in that have already been taxed at marginal rates - from concessional contributions which have been taxed at 15% on the way in (a discount to incentivise saving for retirement via this structure, although they don't let one put much in these days) and the earnings on these funds have already been taxed at 15%.
If one has saved $10M into a bank account and decides to draw out $200K a year from their own capital - should that be taxed? No, only the earnings on the $10M are taxed as it should be.
I agree that the 0% tax on income of the fund in pension phase is very generous - but maybe that it is the reward for putting funds away to fund your own retirement rather than spending it on the high life whilst young and going on the aged pension.