What is the main reason behind the decomposition of microservices?

provide to Scale Independently.

▪ Main benefits of microservices are "Independent Scale and Deployments".

▪ Clearly identify microservices which parts could be required independent scale and deploy.

▪ Design Principle: Decompose services by scalability requirements

▪ Applications are consist of multiple modules or services, with different requirements for scaling.

▪ Example: Our e-commerce application have a public-facing website and a separate administration website.

▪ 2 services required different scalability requirements

https://medium.com/design-microservices-architecture-with-patterns/decomposition-of-microservices-architecture-c8e8cec453e