That is the License or the right to play that game. If you owning the game legally means owning the IP and thus all the rights for that game. This license is physically tied to the disc. Therefore when you sell the disc, you are simply selling your copy of the license. This is wh duplication is illegal if you are selling both copies because you are creating another license.

When the license is tied to an account, that account can have the license revoked. Thus regardless of whatever disc you use, you won't be able to play said game. And reselling the disc will be worthless cause it would not have an account associated with it. Or rather, your account would be associated with it.

In fact, this is also the reason why console versions of said game can't be played on a different console.

I.e COD for Xbox, is a license to play COD on the Xbox Platform, therefore it cannot be played on tthe PS or Nintendo platform, because the player does not own these licenses.

The ONLY difference between physical and digital games is that a digital game is a digital license as opposed to a license tied to a physical disc. The license itself is digital. This is why if you own the game and not the console, it is just a hunk of decorated plastic.

This is in response to the bold part. That's rarely done with consoles and it's highly frowned upon. MMO's are really the only ones able to do that on consoles. MS tried that with the xbone and it greatly backfired on them. 

To the second bold part. Wrong. The differences (yes, that's plural) between physical and digital games are...

You can't legally resell, trade-in your digital copy but with the physical copy you can. You can't sell something you don't own, right?

DIgital copies are not collectable but physical copies are. 

Digital copies are locked to an account but physical copies mostly aren't. 

If you are banned or locked from your account, you can never download your digital game again if you delete it and in some cases, you can't play the game again on that account. Physical copies for the most part don't have this issue. 

Digital is anti-consumer and physical is not. 

I gave plenty of differences between physical copies of games and digital copies of games when you said there's ONLY one. I could of gave you more examples of differences between the two but I have other threads to post and converse in.  Digital games will never be the future of gaming. An option or alternative to physical copies, yes but never the sole choice.