As a crew member, finding an item on board once all pax have disembarked is crucial for security reasons. It would be a major breach of security for a crew member not to hand it in but keep it with them on the return leg as it could be anything disquised as a PSP.
The reason SLF are reminded to remember to take all their personal belongings is not for their own convenience but to decrease incidents of finding unclaimed suspicious items on board, be it in flight or on the ground.Therefore I very much doubt it would have crossed that cm's mind to keep it, cant speak for cleaners but airport staff are so busy that sometimes lost items get mislaid for genuine reasons.
