Niche skill
For almost ten years, I was employed by a software company specifically so that none of the developers would have to write user docs. Just me.
Which was fine when there were only a dozen of them, but by the time I left it had grown to over 50 developers, and I had only the haziest idea what most of them were doing.
Microsoft's documentation is, of course, unspeakably awful and completely impossible to navigate. Google's is, if anything, even worse. I'm glad they both recognise the value of having someone who actually gives a fuck, but I'd be gladder if they extended the scope to cover both those companies' range of products.