One problem is that the idea of being "well-structured" has gone overboard at some point over the past 20 years in many companies. As a result, many companies now operate highly convoluted monolithic systems that are extremely difficult to replace.
In contrast, a poorly designed microservice can be replaced much more easily. You can identify the worst-performing and most problematic microservices and replace them selectively.
> One problem is that the idea of being "well-structured" has gone overboard at some point over the past 20 years
That's exactly my experience. While a well-structured monolith is a good idea in theory, and I'm sure such examples exist in practice, that has never been the case in any of my jobs. Friends working at other companies report similar experiences.
In contrast, a poorly designed microservice can be replaced much more easily. You can identify the worst-performing and most problematic microservices and replace them selectively.