[gliese1337]

Because C is the de-facto standard for writing operating systems.

If you want to write an oh-cool blog piece for general programmer audiences about how OSes work, sure, go ahead and write it in Python (seen that done, and pretty well, in fact).

But if you want to prepare people to be able to work on real operating systems, they need to know how to do it in C.

[something123]

I think an OS class isn't meant to prepare you for working on the operating system. The vast majority of people that take an OS class aren't going to work on OSs, but they should appreciate how everything works. Using a language optimized for communicating "how everything works" clearly should be a priority!

[argonaut]

Yes, and that language is C. C is a very simple language, and it's very clear. If you're writing anything that interfaces directly with the OS, you'll need to know C.