The wear can be from a number of things, such as how many miles a year / month are you putting on the car (which shows wear from the constant driving), how are you driving habits (can relate to "spirited driving" or speeding, which constant rapid rotation of the tires in a giving time frame can very well contribute to the wear) and if you have gone over 1k miles here and there for balance and rotations plus alignment.
My Potenzas that came from factory on my Speed lasted about 18 - 19k miles WITH spirited driving and miles I was putting the car (put about 20k miles in one year on my Speed with 3 Trips to LA and back to the Bay Area). Also, when you purchase your tires, you want to keep track of the wear and performing ratings for the use of the vehicle.
My Potenzas that came from factory on my Speed lasted about 18 - 19k miles WITH spirited driving and miles I was putting the car (put about 20k miles in one year on my Speed with 3 Trips to LA and back to the Bay Area). Also, when you purchase your tires, you want to keep track of the wear and performing ratings for the use of the vehicle.