Today, “network device management” means different things to different people, and the reality is that IT organizations do it, or at least do what they consider network device management to be, to vastly varying degrees, including some who do none at all (hopefully this isn’t you).
At least part of the reason network device management has become such an ambiguous thing is because what we consider to be a network device is constantly evolving. At one point, network devices were largely just routers and switches. Back then, even if one added end-user workstations into the mix, things were fairly simple.