Just to play devil’s advocate… even though the hamburger menu violates several basic design principles, it’s become an established pattern that people recognize. So that counts for something. A lot actually. But that’s not the best defense.
Indeed, the numbers do indicate that you lose out on engagement due to discovery problems. But this is largely an issue for apps that focus on content consumption, which include all the cited examples (Facebook, YouTube, Spotify.) What about services like Uber where there is one core experience and several “utilities” that the average customer will never need to use? Exposing navigation in this type of service is actually detrimental because it makes it too easy for people to forget why they came to the app in the first place (in Uber’s case, it’s most likely to book a ride, not update their credit card.)
While I completely agree that hiding navigation comes with a cost, it also comes with a benefit.