They had to because there was nothing else to wear. When the necessity of wearing animals skins disappears, the justification disappears. Dog carts were an old tradition too, but society progresses and adjusts its ethical standards. Even polar expeditions don't use fur coats anymore, because there are better, less expensive, warmer and lighter alternatives available. We also wear leather.
Leather is a by-product of the meat industry.
Although more and more people choose a meatless diet, as long as people eat meat there will be leather. Alternatives to leather shoes are more difficult to find. The same objection as to fur applies to leather like snakeskin and alligator. Leather lounge suits and coats are, of course, not really necessary either. The meat of these animals is often eaten.