It’s mostly about using every last one of the cpu cycles efficiently, which is old school think from the days when 640k was supposed to be enough for anyone. When I was a wee tyke in the 8bit era we had machines that did graphics, but they were for launching games from a terminal/console.

There are many servers with GUIs, primarily Windows servers, and there’s probably web or GUI interfaces available for every useful service you can run which will be handy in some contexts, but there’s a kind of speed and simplicity you can get with a good console that no gui can touch. Hard to explain unless you’ve done some work.