They're also supposed to extremely safe during a fire but that's only been true in practice for maybe a decade. I doubt ships are hosting many long-lived colonies, but they have plenty of opportunities to get on-board and slip away, and it only takes a few mistakes to end up with droppings or corpses somewhere. I would not be surprised if this led to a "shocking revelation" that sanitation protocols weren't actually being followed and there were a bunch of non-specific systemic issues in enacting them that implicate nobody.