While working on a project with a tight deadline, I've needed complex functionality that wasn't well-documented, and I've needed complex functionality that wasn't there. When it wasn't there, I was forced to produce complex functionality that wasn't documented. If I'm generous enough to release that for others to use, reference, and modify for free, then the last thing I want to hear is somebody bitching about how I didn't document it well enough for them. I have other things to do, and for me it was a one-off project.
In a pinch, source code is documentation, and it's pretty hard to make an argument that undocumented source code is worse than nothing at all. At least then when you're implementing your nicely-documented tool (because you'd rather have documentation than get stuff done), you'll have a reference implementation to look at and test against.
Note: I'm not arguing that documentation isn't important, I absolutely agree that it is. I just think it's absurd to rank the importance of documentation above the stuff that it's documenting.