Some people want paper navigators. Other people don't care about paper navigators and are happy to use the app. Some people choose to use only the app and don't want additional paper that they won't use.
It appears that people on Disboards are more likely to want paper navigators. That could be because people on Disboards are also more likely to be either repeat cruisers, who know how valuable the paper navigators are, or dedicated planners, who want to make sure they know everything going on. People who haven't seen the navigators before and haven't learned about them from pre-cruise research (which is a significant portion of cruisers) won't know what they're missing.
Disney Cruise Line must have determined that enough people don't care about or don't want the paper that they didn't need to produce enough for every stateroom every night. I'm sure they are monitoring how often people ask for paper navigators at Guest Services, and how many are picked up when readily available. If the number of requests becomes onerous, they may go back to delivering navigators each night. Clearly, in the past 6 months, it hasn't been onerous enough to change, and they are still working on matching supply and demand (hence, the stacks of navigators for craft activities).
On our Mediterranean cruise in June, there were always navigators available in a rack at Guest Services. Since I walked by several times a day for dining and activities, it wasn't a problem to pick one up. I would have preferred to find one in my room after dinner, but even in past years when that happened, I would usually pick up an extra so I could carry one around and leave one in the room for my family to reference.
One downside to printing out activities the night before is that if activities are added or changed (for example, due to weather or inability to dock at a port) the Navigators would need to be reprinted. Online listings can be updated more quickly. This is a real advantage for everyone of using the app and decreasing reliance on printed navigators.
While it is true that some people don't have smartphones and therefore can't use the app, the number of such people (and especially the number of such people who can afford Disney cruises) is decreasing. If people can't or choose not to use the app, they can still get access to printed information, just as people can maintain physical address books if they don't want to store numbers exclusively on their phone. (I do that.) I would prefer to have current White Pages and Yellow Pages book for areas I want to call, but the companies that used to provide them have apparently determined that the benefit doesn't excede the cost.
