It's often easier to keep the logbook at the school so that it is filled in at the end of each lesson rather than the student leaving it at home and then work to do to fill it all in approaching flight test. Also if CASA do an audit they need to see them. There is nothing sinister about it, the student can collect it at any time.
It IS your property so no liquidators should be throwing them out. The name and address should be in each one so they can return it to the owner. Not unusual to hear of them going into skips along with student files though.