because the more traffic that affiliates send with a snowballs chance in hell of making a sale, the more money they'll make with the exit traffic they sell to someone else.
No, but really, figure if couple big sponsors have promos, then makes the others sort of have to so they don't lose traffic, so they compete and try to up one better than the other & come up with an equal or better promo..
Sure sales are slower, but they gotta get more traffic to make up for it I guess