I have a couple of decades of experience with real life projects. None of which featured diagrams in the last 20 or so. From extensive interactions with colleagues and friends I know for a fact that this is the case across the board. I have no counter examples. Maybe I live in a weird bubble where people just don't do these things. You know, companies like Nokia, Here Maps, and a few others. Most of the startups in Berlin, or any of the various companies I've visited in the US over my career. Just not a thing anymore.

It was once of course, and unlike most people in this thread I actually did some case studies at companies that proudly showed me their work in the form of lengthy architecture design documents featuring lots of high level and perfectly useless diagrams. That's the reason people don't do this anymore. It's a lot of effort and you don't get a whole lot in return. Doing case studies like this is hard and thankless work BTW.

I spend way too much time looking at architecture documents and then learned more about the documented systems by actually talking to the persons that wrote those documents in about 30 minutes. These documents were basically stating the bleedingly obvious and omitting everything else. Anything actually complex or complicated was left out because it would quickly become unwieldy. A person can tell me that there is a database and it has 20 tables. Or they can quickly tell me what their domain is about and I can infer that they probably have database with things called users, addresses, etc. You don't need a diagram for that. And things like model classes are usually pretty straightforward to read. And unlike the diagram they are actually complete, not out of date, and not overly simplified.

Diagram tools are still sold of course. But it's a niche market. The exclusive customers for these tools tend to be mid to large sized companies where this is a necessary evil to keep their customers or managers happy. It's a form of ass coverage. A chore where somebody has to sit down and do that. No OSS project I know of, small or large, includes diagrams in their documentation. Not a thing. Never has been. And yes, I did some case studies of those as well back in the day. Much easier than corporate case studies. If you don't believe me, try finding some diagrams on Github. I'm sure you might find some but I doubt you'll be very impressed.

I've seen plenty of engineers ask for diagrams but always in this form "someone (not me, obviously) should do a diagram to make my life easier". It's write only documentation. Outdated almost immediately, and typically rarely looked at. Skip it if you can, minimize your time spent on it if you can't. You have better things to do. Software architect is no longer job title that is common or fasionable.

Empirical research in the software world is like architecture diagrams. Lots of people asking for it, not a whole lot of people doing empirical research. And lots of people confusing marketing material with proper research (e.g. most articles published on Agile methodology). And even fewer researchers that even do a half decent job when they do it. It's hard and typically not covered in computer science degrees. So there are a lot of not so skilled, amateur empirical researchers doing a not so great job of doing empirical research. And of course companies don't actually like their dirty laundry being published.

I know this because I was such an amateur researcher and I read a lot of papers back in the day. Like thousands. Part of the job. Most of those papers were entirely unremarkable. The better ones exceedingly dull reading material with inevitably very unremarkable/predictable conclusions backed up by really impressive research methodology, statistics, etc.

The reason I left academia was that I realized that I was not a great empirical researcher, was probably never going to become one, and did not know a whole lot about software engineering and architecture either because I had never worked outside of a university. That's 2 decades ago.

Thanks for asking.