Xbox disc to digital global access when?

That's because your games do not run off your disc.

Not even the ones you only own on disc.

You use the disc to install the game digitally to the Hard Drive of your XBox ONE.

Then because it's a disc copy that acts as your Digital Rights Management and allows you to play the game that is installed on your Hard Drive..

When you own the game digitally only this DRM allows access without the disc.

For consoles if you have a physical disc, the game is never locked. Whoever has the disc has access to the game. It is only a one time thing when the game is purchased digitally.

The games have been delisted. If you don't already own them digitally you cannot access them without an Xbox with a disc drive and a disc

On Xbox One, the entire game must be installed to the system from the Blu-ray game disc. Once it is installed, the disc is only accessed to verify ownership.

On Xbox One, both the digital downloads and the discs are exactly the same size. It's actually a rather neat feature of the system. If a friend installs their game from disc on your system, then when they go, you buy the digital version, there's no download
as the game already installed is simply unlocked to run without the disc verification. Very useful if your Internet connection isn't too snappy.

The code is only needed if you preordered a physical disc from a retailer. If you preordered digitally you will automatically be able to access the beta when it launches.