Why do we still have physical books, newspapers, magazines, movies, music?
While I don't agree with the idea that gaming will be "100%" digital (100% of anything is a big difference from "vast majority" if we're being literal), I will say that one major difference between games on physical media, and other items on physical media is that with games there's not any sort of real advantage or different feel to the actual enjoyment of the work when it comes to "physical".
Book content inside, say, a hardcover coffee table book vs. reading it on an iPad is a very different experience. Movies routinely have extra quality options on Blu-ray vs. digital/streaming. Music on vinyl has a different sound and feel. And so on. But with games, pretty much all the physical benefits are things that have to do with reselling and packaging and how the game data gets onto your console, and nothing to do with the game itself. God of War on a physical disc doesn't have higher quality textures or play any differently than God of War downloaded from PSN, for example (in fact, the "physical-only" version is often worse quality, since it's generally static and doesn't get any fixes or added content).
Video games themselves are inherently "digital", so it would make sense that they're interpreted differently. In a hypothetical world where disc media doesn't exist, the actual art form of gaming doesn't suffer, from a quality perspective. Sure, gaming can still very much suffer from external business and political decisions, but there's no technological drawbacks or loss of progress that would occur with games if physical discs completely disappeared. In addition, for some "emerging markets" that don't really take part in console games currently, physical media could be argued as getting in the way of progress (if someone just owns a phone or a tablet, how is a slavish devotion to plastic discs benefiting them?)
It's why I personally don't have any sort of desire to hold onto physical discs so tightly when it comes to games. I agree that bandwidth caps, DRM, lessened resale rights etc. are issues, but ultimately, those issues need political solutions (I have some fun theories with neoliberalism that I could apply to this discussion as well, lol).