The only reasons I care about discs on consoles is (a) because it allows me to buy the game cheaper at launch than the digital version direct from the console's store front; and (b) it gives me something of value to sell on a later date or to include with the console when I sell it. The download sizes are not an issue as I have a 1 Tbps unlimted fibre connection.
On PC, I frequently buy new games from the likes of CDKeys at much lower prices than Steam et al and rarely pay full price for games. This means that I buy a lot of games because they are so cheap. On consoles, that wouldn't be an option and I would be locked into paying £60 or £70 for new releases that have no resell value. Yes, Sony and Xbox do have sales but they are not discounted anywhere near as much as PC games and new releases will always be full price.
And, yes, Microsoft are going to (and do) ship codes inside a box so technically it will still be possible to pick up their games cheaper from a third-party store such as Amazon or GAME. That is fine but the box itself then becomes useless plastic waste and you cannot sell that on later.