I've seen the opposite: single monolithic codebase, where the different bits of functionality eventually end up tightly coupled, so it's actually pretty difficult to extract bits into a separate service later, so a different type of architecture isn't possible even if you wanted to split it up.

Why do that? Well, when a big Excel file is uploaded to import a bunch of data, or when some reports are generated, or when a crapton of emails is being sent, or when batch processes are sending data over to another system, both the API and the UI become slow for everyone. Scale it vertically, would be the first thought - for a plethora of reasons, that doesn't work. There are bottlenecks in the DB thread pool solution, there are bottlenecks in the HTTP request processing, there are bottlenecks all over the place that can be resolved (for example, replacing HikariCP with DBCP2, oddly enough) but each fix takes a bunch of time and it's anyone's guess whether something will break. Suddenly updating the dependencies of the monolith is also a mess, something like bumping the runtime version also leads to all sorts of things breaking, sometimes at compile time, other times at runtime (which leads to out of date packages needing to be used). Definitionally, a big ball of mud.

Can you just "build better software" or "write code without bugs"? Well, yes, but no.

I've seen plenty of cases of microservices also becoming a chatty mess, but what strikes me as odd is that people don't attempt to go for something like the following:

  * keep the business functionality, whatever that may be, in one central service as much as possible
  * instead of chopping up the domain model, extract functionality that pertains to specific types of mechanisms or workloads (e.g. batch processing, file uploads or processing, data import etc.) into separate services, even if some of it might still use the main DB

Yet, usually it's either a mess due to shoving too many things into one codebase, or a mess due to creating too much complexity by attempting to have a service for every small set of entities in your project ("user service", "order service", ...).