All of the above. But as someone who writes documentation let me add, most programmers are bad writers.

To write good documentation you need to mix technical reference (the easy part) with user reference. The latter requires you to imagine where the user is at, and take them to where they understand. This is hard to do, and requires well, skills.

So a culture of documentation is great, but quality matters as much as quantity. Clarity, completeness and coherence are all legs of the stool.