As far as I know...

Attachment is the 'normal' that should happen as
a child, between parent and child. Forming the correct attachment or bond. Abandonment is what a lot of abused people have been through, why they might be in therapy etc... That's very painful and doesn't lead to good mental health. So the therapist is working on good attachment. When the therapist goes away and client reverts back to abandonment, we need the reassurance of the attachment. The therapist focuses on what is good, normal and healthy healing.

Ok, I hope I've explained it right.