A monolith architecture is one that keeps all resources in one big server. This is something that isn't necessarily beneficial, because if one aspect of this fails, then this means that the entire monolith will go with it. In addition to this, trying to make code changes can be a difficult process because the entire platform would have to compile in order for the change to be complete.
One of the benefits that microservices bring to the table is that since each of the different functions can be separated across the network, if one function was to have an error then it wouldn't affect the other parts of the system. One of the biggest benefits to a microservice is its simplicity. When applications are split into smaller fragments, it is much easier to build and maintain. Also, managing that code that's written is much easier since it is all split in to separate chunks.
Ultimately, microservices make big solutions for problems much easier and allow for more flexibility between teams. The use of microservices is not all beneficial, but for bigger projects, the need to frequently update individual parts of a systems is best coupled with microservices as opposed to monoliths.