Sometimes I wonder if it's a respect or control issue. I once worked in a non-technical position that interfaced with a complex order management system. We were given zero access to documentation and had to rely on trial-and-error and the reverse-engineered model held in the head of one specific supervisor. I'm almost certain that certain errors that appeared over and over were caused by us temporarily clearing previous ones incorrectly. This was especially frustrating because we were 2nd shift, so dealing with those errors could mean the difference between getting home that night or getting home the next morning. It was hard to tell where along the line between, "They're not sophisticated enough to make use of them," and, "We don't want our processes leaking," we fell, according to the higher ups.
My mother worked in engineering back in the late 80s until early 2000s and always told me about people who didn't document things because they wanted to be un-fireable. I didn't believe her or take it too seriously until some of these more recent teams, but I think it is a lot more common than it should be.