It's not something to be taught. For majority of devs an average working day is too short to do everything they theoretically should. So they make choices based

It's not something to be taught. For majority of devs an average working day is too short to do everything they theoretically should. So they make choices based on feedback/motivation which rarely favors writing good docs over writing more code. On top of that many good devs are simply unable to write comprehensible documentation because its very different kind of skills, or just because English is not their native.