When something goes wrong in a system, the concerned stakeholders will want to know what has happened, why it has happened and any hint or clue for fixing it, and how to prevent the same problem from occurring again in the future. This is one of the primary uses of monitoring. However, monitoring spans well beyond this primary usage.
In .NET monoliths, there are multiple monitoring solutions available to choose from. Also, the monitoring target is always centralized, and monitoring is certainly easy to set up and configure. If something breaks down, we know what to look for and where to look for it since only a finite number of components participate in a system, and they have a fairly long life span.
However, microservices are distributed systems and, by nature, more complex than monoliths. So resource utilization and health and performance monitoring are quite essential in a microservice production...