It's a very valid criticism of diagram "systems" like UML. But, "read the code" doesn't scale. It makes it brutal when onboarding new team members who will not understand the "tao" of the system without a fireside chat with the original developers. And, usually, the OG devs are long gone...

Seems like someone asked the same question just 3 days ago. Here is the discussion if you're interested: https://news.ycombinator.com/item?id=31569646

I always had the same feeling, and I found out about aphantasia in the last few years: I do wonder if these are related?