It's an opinion based on countless of references and books out there. I cannot cite them, but it's like "code should be designed to depend on abstract interfaces instead of a concrete implementation", "everything is a byte stream", "adding more people to a late project makes it later", "Bad programmers worry about the code. Good programmers worry about data structures and their relationships", "Show me your flowchart and conceal your tables, and I shall continue to be mystified. Show me your tables, and I won't usually need your flowchart; it'll be obvious.", etc... they are usually true.

> In any case, I believe a DB per backend service isn't a decision driven by the frontend - rather, it's driven by data migration and data access requirements.

I think the idea of breaking up a shared enterprise DB into many distinct but communicating and dependent DB's was driven by a desire to reduce team+system dependencies to increase ability to change.

While the pro is valid and we make use of the idea sometimes when we design things, the cons are significant. Splitting up a DB that has data that is naturally shared by many departments in the business and by many modules/functional areas of the system increases complexity substantially.

In the shared model, when some critical attribute of an item (sku) is updated, then all of the different modules+functional areas of enterprise are immediately using that current and correct master value.

In the distributed model, there is significant complexity and effort to share this state across all areas. I've worked on systems designed this way and this issue frequently causes problems related to timing.

As with everything, no single solution is best for all situations. We only split this kind of shared state when the pros outweigh the cons, which is sometimes but not that often.