Some devs will take interest to documentation but most wont. Most seem to just do a single mind-dump and call it good, no better than the college essay they got a C on. There's also real value in having someone own the organization of the writing.
Maybe a bit over-simplified: SW-Devs talk to the machines, Doc-writers talk to the people. If you can't make the machines understand what you want it to do, you fail. If you can't make the people understand what to do with your precious developed system, you fail.