It's sad. All you can do is try to keep the door open so they can seek you out if or when they do need it. Some people really struggle having good people in their lives because it is so foreign to them and sometimes it can feel like too much attention on themselves when they just want to feel invisible rather then someone who is noticed. It's much easier to trust that people will be bad for them at some point then trust that people will be beneficial for them. People with trauma want to see what they are getting..it's easier to go with what you know than an unknown.
I've found it helps to be extra personable and share little.faults about myself. It tends to put them a little more at ease.