Lack of documentation doesn't only affect open source
I have seen it time and time again, by those who get _paid_. I'd say 70% of the people I have worked with disdain documentation. They usually find some way to weasle out of it. If and when the code or a process is documented, 90% of the time it's just a pseudocode outline of what the code is doing or the repetition of the labels on the screen. I don't see why it was done, what the tradeoffs are, what the impact of a choice is, etc. Basically 90% of documentation I have encountered in commercial products is useless drivel put there to check off the box.