There's no reason they couldn't have both...
Buy a physical disk? Trade use it like you always have, but you don't get to make use of all the fancy cloud features.
Buy your game online? You'll need to phone home every once in a while (24 hours was a bit harsh, maybe more like 1 week), and you can't trade it like physical media, but you get the fancy new lending features.
Decide you like the new way better? Convert your physical copies into 'cloud' copies and throw out the disks.
They had two choices:
Require an internet connection before running a game. (the 24 hour check)
The disk must be present at all times.
1. Converting to cloud could require users to trade in the physical disk at a local store for a digital CD key. A pain for users but by making this a known requirement up front, users won't be able to complain about it and it may convince users who are on the fence to just get the digital copy from the start.
2. Require all games to have a CD Key (acts as the same key for converting to cloud) and a small footprint installable component. Tell users that you don't need an internet connection to validate but if you do connect to the internet, the Xbox One will periodically "phone home" and check to see if your CD keys are legitimate. It won't stop sharing the physical copy after converting to cloud, but it would make it much more of a hassle and prevent multiplayer games from being shared easily. Bonus for users who are converting - the digital version of the game can be installed via the disk so they don't have to wait to download the game to convert it to the cloud. This would also make reinstalling much faster so long as users keep the physical copy.
There are many other possibilities that have been mentioned already so I'll stop here. Just note that this isn't an either or situation. There is a lot of flexibility here.
Or, you know, just turn off the always-online or check-in-each-24h requirement and just lock down the hardware from sideloading games onto it. Even without that, something tells me people would still buy games.
Alternatively, sell your physical disk used and buy the digital copy off live.
Analyses like these seem to forget how much the software of consoles has changed over the last few years. This next generation likely to evolve much faster. The hardware is already obsolete, and it hasn't been released yet. The software is what matters, and it will change. Both Microsoft and Sony have clearly stated that they intend to grow their server farms and make them integral to the experience. So whether you're connecting to Smartglass 2.0 or iPSN, the experience in seven years will not be the same as the experience today.
I found physical media authentication unnecessarily cumbersome in the 90's. It's pretty funny that it's still necessary in some cases, but that's DRM. Too bad that just offering incentives for connecting to official servers isn't the standard means of encouraging legitimate sales. People are lining up for content they could easily get for free on services like Netflix, Spotify, and Steam because they provide superior experiences. I've never downloaded a legally questionable game copy, but I'm still not interested in these backward console DRM schemes, whether through fragile optical discs or constant surveillance. I can do better elsewhere. But I'm looking forward to what they come up with next.