This might be a case of familiarity blindness; people working on GIMP might have come to implicitly assume that destructive editing is a feature, but in reality destructive editing is something only done for resource constraints, not because it's actually good. That's why non-destructive editors essentially never grow destructive features, while most destructive editors tend to grow and expand their non-destructive features.

If you want to argue this from first principles, it's actually very easy: One of the first principles of UX is to respect the user's work. Destructive editing is pretty bad at that. qed.