Many businesses have a Technical Publications department that is in charge of writing software documentation. Most customers never read software documentation. Those two facts are directly related.
Technical Publication Departments Are Ill Equipped to Create Software Documentation
Tech Pubs have almost no interaction with actual users. They create "requirement" documents from the various stakeholders (marketing, compliance, engineering, sales, service, support, etc.) and then create documents that meet those requirements.
Unfortunately they rarely ask users what they need.
This lack of direct connection with end users means that tech pubs has no idea what information is actually important to their users. They don't know what questions the users have. They don't know how best to answer those questions. The end result is software documentation that meets the requirements of "stakeholders" but not users.
Guess what? The stakeholders aren't going to use the documentation.
Your Customer Help Desk Has the Questions and the Answers
The people who are best equipped to write your software documentation are those that are working the customer help desk. They may not have training in technical writing but they know exactly what the most important issues are for your users. They know what *questions* need to be answered. They know the *real answers* to those questions.
Have your help desk people write your software documentation. Their daily interaction with users will help them write documentation that is much more useful.