Sforno on Exodus 22:14/ספורנו על שמות כ״ב:י״ד

1אם בעליו עמו, during the time the animal performs the work for which it has been loaned out.

2לא ישלם, the borrower. The reason is that under most circumstances, the animal has been loaned after both parties had agreed what kind of work it would be used for. Its status therefore is similar to that of a gift on the understanding that it would be returned. When one makes this kind of gift one does not draw up a list of conditions pertaining to the precise use the gift may be made of. If such a list of conditions had indeed been drawn up the nature of the entire transaction would have been nullified, it would no longer be classified as a temporary gift at all, but the owner would remain effectively the owner, so that non return, even deliberately, would not constitute a dereliction resulting in his being entitled to compensation from the “borrower.” The presence of the owner during any accident which had befallen the loaned animal is taken by the Torah as proof that he had never relinquished any part of his ownership, hence he is not entitled to compensation. One does not get compensation for losing what belongs to one.