From the point of view of the social worker in an emergency room, or a psychosocial counsellor in a shelter, or a police officer who encounters a homeless veteran, you don't know who to contact. You may not understand military culture, you don't know the questions to ask. You don't know how to identify a veteran, and once you do, whom do you call?
The flip side of looking at this is to think of the civilian service providers at the community level working with veterans, who don't know whom to contact to work with veterans, how to identify them, and how to help them.