I suspect they arrived at this through a series of A-B tests, since the more useful navigational information they display, the easier it is for the user to "learn" a city, and be able to navigate by themselves. So hiding information that allows the user to learn the map layout probably increases usage metrics.
A couple of years ago I noticed I missed precisely that: "learning" the layout of a city when I travel. So I started using Organic Maps, which always shows street names and other useful information to assist me in my navigation, instead of guiding me turn by turn.
Search results are a lot worse than Google Maps, and the routes it picks are also often worse, and it's missing traffic information. But when I'm travelling I'm usually on foot, and I'm there to get lost and discover the place, so it's OK if my route is not as efficient as it could be.