Perhaps, they employed new people to replace the old. It's easy to imagine some young one, not very smart but full of enthusiasm. And to show his enthusiasm and how he is progressive before his bosses, he presents himself as an inventor! He tells them smth like, 'Hey, it's a thing of the past, we should move forward, no one can stop the change. Look, X, Y, and Z (influencers) have already done that, why can't we be as good as them?' And out-of-touch bosses could think, 'Hmm. There's smth in this guy's arguments. He's young, must be responsive to how life changes, etc.' And voilĂ , catch some new, shiny... s#*!, yeah, but hey: it's new and shiny.
Also... Seems nature doesn't tolerate perfection. Saber-toothed cats, they were on top of the food chain, and what? Beautiful cars, sophisticated architecture, movies with people that act. Phones with buttons. Sites that are pleasant to use. By some reason, all of that has a short life. No idea why ugliness is more viable. May be it's like driving across hills: you are either moving up or down, but it's only a moment when you're on top of the hill. But it's a strange explanation for global things, though.
By the way, these huge empty spaces on the new UI. I doubt they are without a reason. Somewhere, some ads are longing for them. Will come with the future updates? Well, that'd be a pinnacle of trendiness, to make Nexus look like a porn site or, say, a russian e-mail page almost eaten by propaganda.