It's also far easier to help someone over the phone/other "blind" medium of communication with a CLI than a GUI, as you can tell them to press keys on the keyboard and read back the output that shows up, instead of asking them to find and click on things - followed by their thousand-word response (a picture is worth...) describing in exquisite detail everything on the screen except for the exact information you wanted...

That's not to say CLIs are perfect for everything, because there are definitely use cases where a GUI makes sense.