Apple is all about hiding non-essential information and functionality. Always has been. This is a consistent pattern you will be able to find in all their software if you pay a little attention. Basically, if Apple thinks something is a power user feature most users will not need then they have no qualms about not making it discoverable. They tend to even go a step further: they may outright hide it, making it impossible for users to ever be confused by it.
I don't think that's a bad design pattern (depending on context and circumstances, obviously, as always), you just have to make the right judgement calls about what's important and has to be discoverable and what's not. This allows the software to be simple to most users while also having some depth for more advanced users. Like always in design it's all about making the right trade offs, though. The devil is in the details.
On mobile apps it's even worse. Swipe up, left or right? Nobody knows.
I'm torn about this - it's annoying that it's hard to discover, but I also hate when an app gets all up in my face about how to use its features - I usually open an app (especially a utility app like iMessage) with a specific intent and having the app interrupt that intent to tell me about itself is annoying.
I also have the perspective of being an engineer who builds interfaces. I think these are just hard problems and these kinds of pain points are inevitable as we continue exploring interfaces. I mean, the door is an interface that has been around since at least Egyptian times, and people still screw up affordance with it (how many times have you pulled a handle on a push door?)
Why not always show the time, like WhatsApp does?