The issue is removing another option for acquiring a game as well as a lack of ownership.

Physical media allows you to do whatever you want with your copy of the game. It allows the market to determine the price of the game instead of just sitting at whatever price they want on the digital store.

There is also the issue of download speeds. There are still many people in the world who have awful download speeds and/or data caps. Those people will lose the option to have the entire game on the disc.