I think we tend to react to being told there’s a diagnosis name for the thing we’re currently doing, but there are situations in which it is both absolutely normal, understandable, and expected that we behave in a way with the hallmarks of a particular pathology and also we are still behaving in that way and could probably use some support.
(On a more bureaucratic note, the other reason to have an actual DSM-recognized diagnosis is because the ghouls running insurance companies won’t cover counseling without it. Giving your therapist a DSM approved name to apply to your deep, life-impacting, and completely understandable grief means they have a better shot at convincing the claims department you actually do need help right now.)