Why do the tires wear so bad on QX56? Tires have been maintained properly. 45T m

the tires that came on the vehicle--Bridgestone Dueler H/T P225/50R22. the tires are wearing bad on the inside and outside but not in the middle. All 4 tires are wearing the same. Air pressure has been 35 psi, tires have been rotated and balanced every 5-6000 miles.