Because if you teach only what's currently available and popular you miss out on the history. That is, the "Why" and "How" of our current state. Think about it - kids today are growing up with touch screens as being commonplace. There's a screen, they think they can touch it and have it do stuff. Laptops, monitors, TVs don't behave this way. If you had people assume everything is touch they'll be sorely mistaken. Moreover, if you ignore what came before you'll lose sight of what the trajectory is. We've gone from typewriters to keyboards to virtual keyboards on touch screens, though keyboards are staying around for a long time. Given that trajectory, does foot pedals, optical scanners, or voice seem more likely as the next way to control devices? Does your answer change if all you know is we have lettered boxes on a screen that you touch? If that's all you knew, wouldn't it be interesting to see a physical keyboard?
Now these are all things nobody would think that a college student doesn't understand. But that doesn't mean that when you program something you forget about it. Just because you are trying to interact with your program with some set of hardware doesn't mean everyone else will. Great, you've written a game that works on keyboard and mouse. I have an Xbox 360 controller. Now what? Oh, you forgot about those, huh? OK, no worries, I also have a PS4 ... oh, you forgot about those too, I see. Well, I have a tablet with a touch screen, that should be close... no, I see I need to both input a key and move with the mouse. Hmm... oh! I have a laptop, that has a touchpad and a keyboard so I'm all set. Yes, technically it will work that way but you'll find the mouse option is much better than the touchpad option.
Now where might this be useful outside of games? OS design, for one. If you have no clue what your program will be used on, how can you even design it? It's equally absurd to design a console/terminal program that relies solely on the mouse/gamepad as it is to write a GUI program that relies solely on keyboard input.