I basically answered it in the edit. 50B is a long ass time to install, that bit of extra time and space is spent NOT playing the game and eats up valuable space for other games or updates. Like I said, that's pretty much one whole game's worth of space. For.A.Patch.
From what I have read, the game downloads at 112GB but installation size is 55GB. Since the installation size is 112GB and that size does not fit on a Blu-Ray disk, then its understandable why you need to download the 50GB for the rest of the game. Probably one of the big issues are the 4K assets that take up a large chunk of the disks space. Either way, the actual total size of your installation whether its digital or physical will be 55GB. This doesn't look like some scumbag move on Activision but instead just the nature of the beast when you have HD assets but not enough physical space on physical media.