Thevenin and Norton equivalence is the stuff of circuits 1. It wouldn't be appropriate to introduce this tool in e-circuits 1, where the primary focus is analysis of primitives like the diode, BJT, FET, and op amp.
Likewise, the digital side of the house has concepts like sum-of-products/products-of-sums, K-maps, and builds primitive logic gates/flip flops up into SSI, MSI, LSI and VLSI abstractions. It wouldn't make sense to introduce these concepts in courses which focus on analysis of LTI circuits.
The tools at an EE's disposal for handling complexity abound; the above examples barely scratch the surface. Context and practice are the keys to retention, and I would posit that a single course which attempts to teach a smorgasbord of them across various sub-domains has little value if only that students would struggle to discover their relevance. As it stands, many students already struggle to see why the Laplace transform might be introduced in a first course in ordinary differential equations.
I was happily surprised to read about Thevenin/Norton rules to turn sub-circuits into a virtual ESR element. Very tree recursive.. very interesting.