If you have a low income and need all the money to buy food you get taxed on 100% of your income. If you have a lot of income and can save or invest 90% you only get taxed on 10% of your income.
If you are low income and they give everyone a tax refund on the first 30k or so of spending, then you perhaps pay 0% in taxes while the person spending over 30k starts paying a tax.