Shit I even made GUIs for all my command-line tools so normal people could use them.
Using the Unix philosophy to combine text based tools does not translated to GUIs. How about test automation?
Back in the day when I was still forced to develop software on Windows or Mac OS I wasted so much time maintaining brittle click & even snoop-based integration using kludgy tools like selenium and add-hoc click-the-freaking-button.exe just because the app originally happened to be developed natively in Java, Flash, HTML5+ajax by some rockstar, 10x coder without seatbelts.
Or try running a simple Java tool on headless Windows using Jenkins agent or cygwin SSH and you'll discover how horribly bad relying on a GUI can be. Or: how about automatically launching a MacOS VM on VMWare and setting up a VPN tunnel after a restart power outage without a mouse, keyboard and display. Should work in theory, but in practice never gets beyond most of the time.
There’s no reason why an app can’t work as well either via command line or via GUI. The whole point of architecturing your software is so you don’t write something kludgy.