The problem is, GUIs usually give you ridiculously low ceiling for productivity. So you're forever stuck with the level of productivity you get right off the bat. It used to be that GUI software had keyboard shortcuts for most operations (in particular, Windows made it really easy to do, and expected you to do it) - but then the web came and it all flew out of the window.
So part of the reason to use TUIs and Unix commands is because modern GUI philosophy makes my mind throw exceptions from boredom in the middle of doing something.
> How many program interfaces can you keep in your long term memory? Is it even worth it to waste your precious (human) memory space in such a thing?
Quite many. Human memory has natural garbage collection, so don't worry, you're not wasting anything. In this day and age, you're not really using your memory to its full natural capacity anyway.
And before someone says that learning a tool takes time, try this experiment: pick a tool with shortcuts you don't like, and spend one Pomodoro trying to operate in it. 25 minutes. There's a good chance you'll be past the mental block in that time, and the new navigation will already start to feel natural.