They’re changing a bunch of things about how the Office apps work. They’re doing a similar thing with Outlook. There’s also now “New Outlook” that they push you towards, which looks a little bit fresher yet is also missing features from the last version.

I’m assuming they’re changing something architecturally about how the apps are put together, but the only thing I’ve actually seen is the bugs and all the headaches that come from migrating everybody to what’s basically a brand new app.