With apple's iphone 8 going back to a all glass chassis, i'm sure they asked corning to develop this because it saves a layer on the phone, therefore enabling it to be thinner than a iphone 4 for example.
It may not have anything to do with the extra space around the screen. The S6 and S7 have glass on the back. With the ever-disappearing phone bezels, I'm not sure that's something the market would want anyway. It's not too much of a stretch to suggest that they might want to add some kind of pattern as a customization option for the S8 and beyond, or they may simply want to have the "SAMSUNG" on the back be in color.