That's not necessarily the case. In fact, if implemented well, keyboard/command-driven UIs can be much easier to discover than GUIs.

Consider the "Command Palette" and similar features that are part of many UIs (VS Code, Obsidian, Vim, Emacs, etc.). It allows the user to search all possible actions using natural language, and see or assign key bindings to them, so that they can get to their most commonly used actions faster. This search can be global for the entire program, or contextual for the current view.

It is far easier to search for what you want to do, than to learn to what action every GUI element is associated with, or to navigate arbitrarily nested menu hierarchies. This does require the user to be familiar with the domain language somewhat in order to know what to search for, but this too can be simplified, actions can have different names, etc. It also makes the program more accessible for speech navigation, screen readers, and so on.