There was news that the new console will be able to sell your used games on the Xbox One.
I think the reason is Microsoft just wants to kill the secondhand market and gamestop and take money for themselves. I bet it's gonna be revealed and clarified that you can sell your license to the game on their marketplace and you earn a certain percentage (if they were nice it would be high like at least 70% but who knows) and you can only put that money back into the Xbox marketplace for a new game or whatever.
To stay on topic, I bet this is why it requires always online, license checking. If you sell your game but never go back online then you can have your cake and eat it too.