Why in iOS is the arrow always only on the Back button?

Question

iOS

Example:

Answer 1

Because Back is a system action. Unless otherwise specified, the Navigation Controller always has a Back button. And the concept of the Next button does not exist, what your right button will do is up to you. If you want to make it with an arrow - make a custom UIBarButtonItem for your health, no one will forbid it. But the system cannot know in advance what kind of action the Next will take.

Answer 2

Because the designers from Apple decided that it was so cool.