I disagree, Out of Band Network Management (OOBM) is extremely trivial to implement. Most companies however don't see the value of OOBM until they have a major fault. The setup costs can be high, and the ongoing operational costs of OOBM infrastructure and links is also significant. I've built dozens of OOBM networks using fibre and 4G with the likes of Opengear. In instances, often deploying OOBM ahead of infrastructure rollouts so hardware can be delivered to site directly from factory, rather than go through a staging environment which adds time, cost and complexity.