The problem is that you don't know who's listening. You don't want all possible interested parties to hammer the database. Hence the events in between. Arguably, I'd not use Kafka to store actual data, just to notify in-flight.
This reminds me of the OOP vs DOD debate again. OOP adherents say they don't know all the types of data their code operates on; DOD adherents say they actually do, since their program contains a finite number of classes, and a finite subset of those classes can be the ones called in this particular virtual function call.
What you mean is that your system is structured in such a way that it's as if you don't know who's listening. Which is okay, but you should be explicit that it's a design choice, not a law of physics, so when that design choice no longer serves you well, you have the right to change it.
(Sometimes you really don't know, because your code is a library or has a plugin system. In such cases, this doesn't apply.)
> Arguably, I'd not use Kafka to store actual data, just to notify in-flight.
I believe people did this initially and then discovered the non-Kafka copy of the data is redundant, so got rid of it, or relegated it to the status of a cache. This type of design is called Event Sourcing.
So yes, in large companies, your development team is just a small cog, you don't set policy for what happens to the data you gather. And in some sectors, like finances, you are an especially small cog with little power, which might sound strange if you only ever worked for a software startup.
Disclosure: I work part time for Oracle Labs and know about these features because I'm using them in a project at the moment.
The messaging tech being separate from the database tech means the architects can swap out the database if needed in the future without needing to rewrite the producers and consumers.