Developers give away their time and brain power for free. Apparently technical writers are less inclined to do so. It's not like developers are unique. Lawyers do probono work, doctors and dentists volunteer at community clinics, accountants offer free tax prep to people in disadvantaged communities, etc. Maybe there are people who would be willing to take developer documentation of FOSS products and turn them into user friendly documents. Pretty sure that already exists for some projects, though some of that might be paid work (which sometimes is true for development work too).