I would say alignment or rear subframe is bad. My buddy with his e46 m3 which is notorious for subframe issues was eating through tires like every 4k. He got lucky and dealer did it under the recall but he missed it by a few months but they took care of him.
You asked how long do they last? I've seen tires last 100k and some tires last 30-50k. MY RFT were shot at like 10k lol I beat them to death since i wanted new tires.
My father x5 E53 went through 3-4 sets of tires and hes at 240k on his SUV.