Why do I need a wheel alignment after each tire rotation 2841

I agree rotating the tires doesn't change the alignment (or at least it shouldn't). However, I have had cars in the past (1986 Sable for one, Mazda 626 for another) that when you rotated the tires, the car would immediately develop a pull. And it didn't seem to matter whether you cross rotated or did a straight front rear swap. As long as you didn't rotate the tires, the car did not developed a pull. After the second set of new tires (came with Generals, I bought two different types of Michelins before I figured out my problem), I just quit rotating the tires on that car. The rear tires would last about 50% longer than the front tires, so I just started buying front tires more often than rears. There was never any obvious strange wear pattern on the front or rear tires. And, interestingly, once the pull developed for a set of tires, I couldn't fix it by rotating the tires back to the original position. I could change the direction by swapping tires from side to side, so I am sure it was the tires, just not sure what was going on.

Ed