The thing is that you are conflating CPU architectures with computer architectures; In academia they are treated as two different educational topics, for good r

The thing is that you are conflating CPU architectures with computer architectures; In academia they are treated as two different educational topics, for good reason. The first one covers the lowest level of how logic gates are physically wired to produce a Turing-equivalent computing machine. For that purpose, having the simplest possible instruction set is a pedagogical must. It may also cover more advanced topics like parallel and/or segmented instruction pipelines, but they're described in the abstract, not as current state-of-the-art industry practice. Then, for actually learning how modern computers work you have another separate one-term course for whole machine architecture. There you learn about data and control buses, memory level abstractions, caching, networking, parallel processing... taking for granted a previous understanding of how the underlying electronics can be abstracted away.