Imagine having a huge monolith application with a lot of complex functionalities strongly tied together. The scalability is a big challenge, the deployment process could become very cumbersome, and, since the internal components are highly coupled, to change the functional flow isn’t gonna be that easy.
Maybe a lot of people are familiar with this concept since this was the standard way to build an application until few years ago and that there are still a lot of monoliths in production these days.