The things nobody wants to pay for

I actually don't think the problem is with companies, or at least not ONLY with companies. In my experience, many companies in the kernel development sphere are more than willing to let developers and maintainers have the time to contribute (and actually do let them contribute) to projects like the kernel -- including documentation. I know I personally have a broad mandate in my role to contribute where I want or where I think it's most important, and I'm sure I'm not the only one.

In other words, it's not companies' fault that their employees choose to spend their "20% time"-equivalent on those "things nobody wants to pay for" -- it would arguably be worse for individual employees if the employer mandated that they work on (say) documentation over letting them have the choice.

I think the question we need to ask instead is, why do people choose to work on code rather than documentation?

The answer -- my answer -- is a mixture of things: Most people are in kernel development in the first place because of the code, not because of the documentation. It was the code that they ran, that they looked at, that drew them in -- not the documentation. Writing code is fun, getting something new to work is exciting, writing new features will designate you as an expert on an area of the code, maybe even get you some (community) news coverage. Useful code ultimately makes somebody money, making developers and maintainers of said code valuable to companies. Code may get your next job (or at least a bonus); documentation, probably not so much.

I believe I've said similar things about code review before: Code review is simply less glamorous than writing said code. If you had the choice -- write new code or review somebody else's code -- one of them has a very obvious and short-term personal payoff, the other one has long-term payoffs for the community at large.

We need to find better ways to incentivize each of these "things that nobody wants to pay for".