Any organization that is not starting from scratch has existing IT systems and infrastructure in place. In many cases, this legacy has issues keeping up with today's demand for how quickly organizations need to be able to adapt and change. One common pattern in larger organizations is "monolithic applications" which often have been around for quite a while and are highly integrated and complex IT systems.
Since these monolithic systems tend to be calcified to a certain extent, they often reflect (and have been painstakingly optimized) the way an organization works currently, but they often also are hard to change when the organization wants or needs to make changes to what it does and how it does it. Microservices often are mentioned as a way to avoid some disadvantages of monolithic approaches, but since many organizations already have monolithic applications around, how can you transition from the old to the new?