What if the major benefit, as a game, is that it can't be pirated?
Regardless if it is a DVD or Blue Ray, the problem is that the player mechanism is always running, inducing it to wear. What people want is to be able to "download," or copy, or install onto a hard disk drive, thereby cutting the load times when playing. Not that that always works even on a PC, mind you. There is supposedly one PS2 game that has load times of over 30 seconds when scenes or levels change. On the PC side there is supposedly a simple graphics game which brings the fastest graphics card to its knees. On the PS2, if the reason for dropping frames is the DVD, then does it drop frames when playing from an HD? Likewise, why install a 5400 rpm laptop drive into game systems when faster drives have faster transfer rates? Well, because the slower speed drives are more reliable vs faster drives. But if the slower drives contribute to frame drops then what good is it?
So, why isn't it done? Because of Pirating, most likely.