Why can’t I see resources I want to add to a SCCM 2012 Direct Membership Collection?

Why can’t I see resources I want to add to a SCCM 2012 Direct Membership Collection?

I am trying to add a resource to a ConfigMgr 2012 Collection based on a Direct Rule. However, the resource I want to add isn’t showing on the Select Resources page of the Create Direct Membership Rule Wizard.