I don't understand it either, but I have had the one canti that is seizing off twice now and can't get it apart to see what it going on, there is a sleeve inside the brake arm that seems to be the pivot for the brake arm and it is here that it seizes. I have tried penetrating oil, lube, a hammer, a screw driver.

I just wanted to get some suggestions on a better brake before I purchase the same problem.