Paper tickets were accountable documents. Blank tickets each had a potential maximum value of some 10s of thousands of dollars/francs/pounds. Completed tickets had the value written on them and, depending on the tariff, could be refunded/rerouted/reissued, without too much difficulty. If you lost a paper ticket getting it reissued required you to indemnify the airline against any loss.
They were expensive to print, to store securely and to transport. Travel agents had to have a safe on their premises.
Lower costs to the airline mean lower fares, not higher airline profits.