Not the person you asked here, but my guess is that it mostly has to do with the need for asynchronous communications. You can't just quickly ask the guy from Japan and expect an answer right away. That means the text needs to cover all questions.

I once worked in a job where each day of the week was covered by a different person. Meaning at the end of the day you had to leave everything in a state that another person could pick it up right away without much hassle. This was mostly done via emails and pieces of paper with text on it, but worked flawlessly.

And the only reason it did was because you couldn't just ask the guy from the day before a question. It all needed to be anwered by the work he left for you.

I’m forced to do this with claude code: documenting work for context management. Every new agent starts fresh, so everything better be recorded and explained.