Why can't I hide Parent Resource field?

Just wondering why the [[*parent]] / Parent Resource field isn’t included on the list of Available Fields for Form Customization for a resource (http://rtfm.modx.com/display/revolution20/FC-Resource). I’d like to remove that field from display for some of my users - I want them to use the tree exclusively for determining the parent resource.

I was facing the exact same problem, and found the solution elsewhere on this forum.

To hide the ’parent resource’, use: modx-resource-parent