[viraptor]

> why I almost never see complete

That's a huge scope question on its own. What's "complete"? How low level or wide do you go? What about the view of internals of the external systems you rely on? What about their mapping to teams/owners? C4 helps a bit here by saying "whole organisation throws everything possible into this and when you want to see it, you use scoped views instead".

> or up to date diagrams

"When exactly does the system change" is tricky too. When you change the code? When you enable the new system? Who knows that the diagram of the system exists and where? It's a bit of an issue of unknown unknowns. Again, the C4 idea helps here a bit, but there are still going to be random projections of state at a given time saved in various places.

Another big issue is that structure and presentation are very different. Generated diagrams of infrastructure or code look shit, universally. On the other hand, well presented diagrams are just snapshots in time that get preserved for years even if their outdated. I mean this is what C4 page shows as one of their results https://c4model.com/img/alternative-1.png which is an unreadable mess and this is what they initially complain about https://c4model.com/img/sketch-2.jpg which is perfectly sized and context specific goodness. The first is good for knowledge preservation, but if anyone needs to understand things, I'm making the second one for them.