Front Suspension Control Arm problems of the 2008 Mazda MAZDA3

Like other Mazda 3 owners, my complaint concerns the rear tire camber. I noticed this condition after the 2nd set of tires. I didn't think that much of it during the first set of tires as the tires lasted for apprx 50k miles. But the 2nd set started to vibrate and rumble loudly after about 12k miles. I had them aligned and rotated but the noise and wear became worse. I purchased a 3rd set and again had the wheels aligned and the set lasted for about 30k miles. But I must state that the vibration and noise was unbearable, at this point. I finally found a mechanic that understood the problem. The rear control arms were fixed (did not have an adjustment). The only way to correct the problem was to replace the control arms (with an adjustable set). The car now rides smooth and quiet. My question and complaint. . . Mazda must have known about the problem, otherwise the replacement parts would probably be the same as the original, nonadjustable. So why, didn't Mazda offer assistance? the repair cost me over $625, not including the prematurely worn tires. I was very pleased with the car until this occurred. Now I question Mazda's integrity and may never purchase another one.