PC gaming is pretty much already without anything physical. Steam and all. Only PC game I still use a disc to play is AVP2.
For consoles people still buy physical copies, if that ends they will lose quite a fortune, some people won't pay the same price to just download it, even now they don't, not when they can download things through cheaper ways. So its better for them to keep that option for those that like the boxes, the gaming industry would probably increase microtransations even more if physical copies go to hell.