The reason Amazon hires any worker, homeless or not, is to extract a profit from their work. It's entirely possible that it offers the exact same conditions as other workers, but to describe it as benevolence is naive at best.
Amazon has a huge surge in orders during the christmas period, and it struggles to find enough workers to keep up with demand. This article makes it clear that this was a scheme aimed at coping with the seasonal surge. It has nothing to do with Amazon wanting to see homeless people better off.