In fact the CLI is easier to understand than GUIs for all tasks that are not graphical in nature.
If you think of it, it is just like chatting with you computer : you ask for something, your computer answers. There is a single point of input and a single point of output : no need to look for menus, icons, etc...
It may not be the most efficient way to deal with common actions, especially on mobile apps, and is isn't very sexy but it is easy.
I think that the reason why people think that the CLI is complicated is that most of the time it is used to do complicated things. If such things were integrated into a GUI, it would likely require some even more intricate path of action.