The same reason students aren't taught version control, or unit testing, or shell scripting, or text editing, or documentation writing, or even (beyond intro courses) programming languages. The class is about computer science, usually a single concept or family of concepts, not programming. You're expected to learn what you need.
This isn't unique to computer science. My chemistry classes (I also have a chemistry degree) didn't teach me how to use any chemistry lab equipment, either. You learned that by hanging around in the lab and watching other students and asking the grizzled old profs who hung out there.
