That uncouples wages from the value of the work performed. It would be more honest for the government to make up the difference between the real wage and the "living wage". If the "living wage" in your area is $15/hour and you earn $7, then you get welfare benefits of $8/hr. Not saying it would be sustainable, but it would be more honest.
Here you go again assuming facts not in evidence. You don't know how many people making less that 15 an hour receive social welfare services.
Try this. If you are so unskilled as to only earn 8 an hour and you need 500 a week to pay your bills then you work a second job so the money you can earn for your skill level is enough to pay your bills. Then you make your labor worth more so you can work less hours and still pay your bills
It is not written anywhere that merely working 40 hours a week will earn you enough to support your lifestyle