This is expected, retaining the context of the original post in the review queue is intentional so staff can see the state of the post when action was taken against it. A user deleting their own post only soft deletes the post, so the original is also retained there (as a revision in the edit history) unless an admin deletes it permanently.
The scrub was necessary in FEATURE: Add scrub action for rejected reviewable users - Pull Request #36556 - discourse/discourse - GitHub because rejected users only exist in the review queue… there’s no where else to go to delete their content.
Admins can permanently delete posts or topics (with the can_permanently_delete site setting enabled), which removes the post, its revisions, and related review queue items.