They're likely speaking of their liability should a employee's laptop, containing sensitive information, ever be stolen or re-sold (or simply, left in the hands of an ex-employee with a grudge.)

It would be difficult for a IT department to guarantee, for sure without replacing the internals of the device, that the device doesn't contain sensitive information. Probably easier from an inventory and IT security perspective to just capture every device than try and coordinate with individuals to reformat, etc.

(for the same reason, some companies outright destroy old devices instead of reselling.)