I find the signal from this is still too low for it to be worth looking into. Quality of documentation has a lot to do with:

1. Correctness

2. Matching the content to the intended audience

I find that in general I have no time to check correctness, nor is it obvious who the intended audience is. A blurb and basic setup instructions is fine if the intended audience is the author. A tool intended for a particular set of power users may not require motivation. The author may well know how to write more accessible documentation and chose not to for a sensible reason.