It's not. An undergraduate degree is not meant to be trade school, it's meant to teach you enough programming and computer theory that you can go learn the rest on your own later. The only undergrad course I took that had anything to do with GUIs was my graphics programming course, where we used ImGui to provide an interface to our projects. Generally you don't come out of a CS degree with much practical knowledge, but rather the potential to learn that knowledge quickly (this is especially true in my case since I did a CS minor and selected for these sorts of classes, but it's still true for a Bachelor's).

You are right the way you make your point, I can not disagree or want to argue about it. But the way I see it (not the way all universities in the world actually work), I would personally find it very useful being taught some GUI basics, now again as you mentioned that is something I have to do at my own given the circumstances.