When you have a car that weighs over two tons, it is reasonable to expect that it will have large wheels, proportionally big tires, and, of course, a spare. Something that size is going to take up a lot of room in the trunk, leaving little room for luggage and golf clubs.
For many years, spare tires were mounted unprotected on either the front fenders or the rear of the car. Someone came up with the Continental Kit as a way to protect the tire from the elements while giving a longer, lower look to the auto's profile and maximizing trunk space. The "big is beautiful" approach to building cars effectively ruled out the idea of reducing the size of the tire until many years later when cars got smaller and it was impractical to fit a full size spare in the trunk. Some new cars have eliminated providing the spare tire as standard equipment.
I'm not sure that is an advancement in auto design.