But what part of their training actually translates in this way?

If a doctor receives training in managing high blood pressure with drugs, they can reliably apply that training to real patients.

If a therapist learns about attachment, I dont see how they can apply that in any meaningful way, since human relationships are not at all mechanistic.

The premise seems to be that a therapist can be taught to orchestrate for-hire relationships according to some formula, then apply that formula when a person with attachment problems shows up.

If a therapist believes they are capable of this on a routine basis, they might have a psych disorder.

Also if a client undertakes such a process, are they to ignore the fact that the whole thing has been contrived? And that interactions, ruptures, repair, trust building, etc are at least partly fabrications and not spontaneous in the normal sense, and that much of the resulting drama and turmoil is process-driven?

TLDR: What exactly is meant by attachment therapy?