Before the internet, the printed book was all you really got. That meant the company distributing the software had to hire technical writers who'd work with the software devs to create all of this, send it to an editor, and ultimately get published.
We no longer live in an era where tech companies hire tech writers. Software documentation lacking is something that can and limp along with jira cases and support services sold rather than trying to put in the upfront effort to fix everything.
Now, for open source software, hate to say it but the docs have always been pretty crap. Certainly some stands out (usually when the business model was around providing services on top of open source software), but nobody is really paying anyone and few people really want to do that sort of free labor.