Because it has nothing to do with BDSM marking - there is no pain involved... or maybe you had a bad experience with a vacuum cleaner trying to fake a love bite as a teenager which you are supressing

The human mind is a wierd and wonderful thing, full of complexity. In some ways it is a perfect example of chaos theory - simple basic responses (I am angry, I am horny, I want to hurt you, I want to love you) produced by underlying complexity.