If everything was tutorialized in iOS itself, it would just overwhelm the user with tons of information.
If it was a part of the post-install wizard, it would get skipped and you wouldn't have the benefit of learning it in natural conditions.
If it was a part of regular use, it would probably come at the worst of times. No easy way there. Tips app is a good solution
Old iOS versions were a lot simpler, without many notable features that we love today and take for granted - Notification Center, control center, iPad gestures, swipe to go back...
The original iPhone had an advantage that it was so simple, all information and control could be just present on the screen at all time. But even a thing so simple as a clipboard needed to be hidden behind a gesture (long-press) - otherwise it would just have to be on screen al the time, obstructing the content.
It is a hard problem to solve. Discoverability versus usefulness.
On the other hand, none of the features that seem to be hidden is crucial. All the basics are right there, visible at all times. Think of these hidden things as shortcuts, which they really are.