Why would a billion-dollar company pay their employees so little that they need assistance to live? Or need to urinate in a bottle to keep their delivery times up? Greed and a belief that the rules don't apply to them.
I suppose if you advertise a job for $20/hr and a bunch of people show up and apply for the job, you're probably not going to start advertising the job for $40/hr instead.
And whether $20/hr is a "living wage" depends entirely on your circumstances. If you're a solo adult you can probably swing it. If you have 3 kids you will probably be on food stamps. Should Amazon pay people with kids more? Or only hire single people with no dependents?
The apt comparison would be wage theft. It's one thing to advertise a job at a particular hourly rate, entirely another to breach the contract and lose public trust for a paltry gain. If you're going to commit what people will interpret as theft at least make sure it's worth your while.