I think the secret reason that so much open source software is designed for CLI use is NOT just that we really like the console, but the deeper and much more true reason is that writing a GUI is a pain
I have written GUIs in more GUI platforms than I can count and all of them make my brain bleed
I have written GUIs in many GUI platforms too, and the only simple ones were original Visual Basic and Windows Forms, so Microsoft killed the first one, and deprecated the second.
Of course, you are right: writting a CLI application is much more easy, much more efficient, and wastes less resources.
But users don't want efficiency or less wasteful applications, they want nice, warm, cozy, trendy GUIs. They may say the opposite, but if they are not using CLI only, they are lying.
