Yes, exactly. Major airlines are going to accumulate a sizeable number of bags which can't be matched to their owner with detective work that is going to cost

Yes, exactly. Major airlines are going to accumulate a sizeable number of bags which can't be matched to their owner with detective work that is going to cost more than the bags are worth. And they can't store bags forever waiting in case the owners use their own detection mechanisms. Paying compensation and donating the bags seems fine, as long as the compensation is reasonable.