This kind of rotor issue is almost always (99%+) a function of excessive heat. If you don't use them in the couple of ways that can kill them with heat, and since you say you've gone through several sets of rotors already, one would wonder if you've had some intermittent caliper sticking issues. That also tends to take out brake pads as well, though. What you haven't mentioned is what your pad condition has been doing all this time. Also, I am assuming front rotors only, but please identify if it's both fronts, and also whether the rears have posed any issues at all over this time.