Modern CPUs are too complicated to teach in a semester. Plus, the course is meant to teach how a CPU works at a conceptual level, not train students for x86 assembly programming.
I had an "Assembly" course in my undergrad that taught x86, we managed in in semester. But it was a separate class from Architecture (and had Architecture I as a pre-requisite). Granted it didn't get into the hyper-optimized / specialized instructions.