The NEC doesn’t consider flexible cords to be wiring methods like those defined in Chapter 3. They fill a different niche; therefore, they are in a different Chapter.
Much of our infrastructure and industry simply would not run without flexible cords and cables. You would not, for example, be able to take an elevator ride or operate a hoist without them. Many types of lighting installations also rely on them, as does a wide range of equipment.
Article 400 covers the