The business sense of NextGen, if it were on budget. Clearly it's been an implementation nightmare but these failures weren't part of the original plans. Obviously they wouldn't have done it if they knew it wouldn't work.
That said, a functional NextGen is based on the notion of creating a packaged experience. Besides benefits for resort guests, as others have mentioned, it encourages guests to pre plan many of their experiences. If you have Fastpasses planned for every day of your trip before you even arrive, you're less likely to decide to leave property. If you're considering doing so, there's a feeling that you're "wasting" that day's Fastpass allotment. You may, in reality, have time to do MK in one day by Fastpassing the mountains and doing standby for the rest, but the psychology of the whole thing indicates that you'd rather "be sure" by planning a second day with Fastpasses for Wishes, MSEP, and Peter Pan. Thus, you fill every day of your trip with your must-dos and all of a sudden there's no time on the calendar to visit Uni. Encouraging guests to view the attractions list and engage with it before their arrival creates a sense of urgency that "ooh I don't think we should do Sea World because I don't want to miss anything at Disney." You and I visit so frequently that we know what attractions we don't mind missing because we'll be back soon enough. A first time or infrequent visitor faces a daunting task trying to do absolutely everything in one week. Even DHS is a full day park if you've never seen the shows and try to catch them all. People are intimidated when planning a Disney vacation. The goal of NextGen is to help manage that overwhelming feeling. They're trying to take people from "screw it, I'll never see everything anyways so I might as well do uni while I'm down there" to " if I take my three Fastpasses per day, I think we'll be able to do everything we want, as long as we stay on property."