Software suffers from poor documentation principally because those who write the code don't have the time or inclination to write documentation, especially if they will have to do it in their own time. Most experienced developers can write well enough but they know that no one will maintain the docs so why bother. In my experience as an internal application developer the documentation is created only when someone leaves or a major application needs to be ported.

Internal software is probably the worst because there isn't a paying customer in the usual sense of the word so there is no one to send the bill to.

Do technical writers still exist? I could write documentation, in fact I intend to spend three days next week doing just that, but someone who has that as their primary skill would do a better job; unfortunately the company no longer employs such people.