It's not so hard to do static and tracing-based analysis to capture all the calls that various systems make between themselves. Similarly, it's not so hard to g

It's not so hard to do static and tracing-based analysis to capture all the calls that various systems make between themselves. Similarly, it's not so hard to graph all of the metrics of a system. That's not really all that useful. Diagrams, like other forms of documentation, are a format for communicating something to the reader. It means that they should spend more space on the important flows rather than the exceptional ones. They'll explain the meaningful parts of a sequence rather than just giving a series of function calls. The various tools we have for doing this (boxes showing what systems talk to what, sequence diagrams, database schema diagrams) provide a rich enough language for that communication. Death star diagrams are bad because they spend a bunch of time and effort to convey one piece of information: "there are a lot of systems here" rather than anything actually useful for someone attempting to navigate a specific part of the system.