Why did Apple remove so many features from the Mac iWork apps? I don’t know, but here’s a guess.
Ive has now been put in charge of human interface for software as well as hardware. He brought a fresh pair of eyes to iWork and saw a lot of things that could be improved. (You might not agree that they are improvements, but I long saw things in Pages that I felt could be improved.) But he also lacked the experience of what customers wanted.
Combine that with the work to bring the Mac, iOS, and iCloud versions of the iWork apps closer together. The decision was made to move forward with these things, but to also—when installing the new iWork apps—leave the current ones installed for existing users who depend upon existing features. That will give them time to reassess those features, to be thoughtful about how they bring them to the new apps, and to take the time to implement them well.