I don't know how you managed to make that leap. Publishers sells more boxed copies because that's what consumers buy more of. If everything went 100% digital, publishers would still be around to publish the games. It's actually a benefit to publishers because there's no used-games market for digital sales and you have no manufacturing costs for boxes, manuals, disks, display stands in Best Buy, etc.
Publishers do a lot more in the process than physically take a disk and put it into a box.