I run across, almost daily, cases of "but we have always done it that way", so sometimes the issue could be unknowing beneficial ignorance. Catch-22 (which I am actually rereading). We may not be allowed or comfortable prying and sharing knowledge, and the needed information may not be shared on purpose or by ignorance.
In your cases, there are things your clients may not share. In mine, it is things such as "I want to pay something to my employees pre tax", with push back when I ask for details on the "plan".