I couldn't make it switch for about 10 minutes of trying either but then i did it for a minute. Probably still couldn't make it switch if i tried now. Once you see it one way it is very difficult to see it any other way because you learn what what you think it should rotate. But my original explanation is why it works. It's that moment when the two legs become one that tricks your brain...that combined with the upper part of the body twisting unusually. It's just an illusion.
I know I am left side dominated from EEGs but I saw the image going clockwise. The illusion in no way suggests dominance of one side of the brain over the other. Hogwash.