Please, anyone, tell me what happened when the Carrion Queens did A LOT more damage than they should? Why is that different from this?
On a purely technical level, I would assume it's easier to move a complete character back from Standard to Hardcore League than restoring individual messed up/deleted items. Implication-wise, well, it was something nobody @GGG was really happy about since they were fully aware of creating a precedence. It's definately not something they'll do again more lightheartedly now that it had happened once.
Generally though: If there's evidence that it was impossible for the player to trade or delete the item themselves, e.g. with an mtx attached then there should be a better way of dealing with this than "nope, sorry". I mean, I'm not a programmer and might miss something obvious but I really can't see any dangers of intentional duping or other exploits here.
Edit: maybe it's a good opportunity to (re-)work (on) some soft delete/backup systems. Stuff like soft deletes for characters has been vaguely promised for ages, there have been quite a lot of suggestions about buy-back options at vendors and characters and items not going *poof* could be useful on GGG's side at some point, too.