When something goes wrong in a system, stakeholders will want to know what has happened, why it has happened, any hint or clue you can give for how it might be fixed, and how to prevent the same problem from occurring again in the future. This is one of the primary uses of monitoring. However, monitoring can also do much more.
In .NET monoliths, there are multiple monitoring solutions available to choose from. 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 lifespan.
However, microservices are distributed systems and, by nature, more complex than monoliths. So resource utilization and health and performance monitoring are quite essential...