Tickets bought at the counter are printed on special security paper. If you lose that, it is as if you lose a banknote. You will not get a replacement from the bank in that case either.
Otherwise anyone could just claim they had lost the ticket, take their receipt to the counter, and get another one printed, and thus get 2 (or more) for the price of one. SBB does not want that to happen obvioulsy.
That is why traditional printed tickets must be treaded as if they were money.