I have issues with this too. In my case, I think it's a combination of sensory issues (hate getting wet, the feeling of water pounding on me (but I never feel quite clean after a bath, like I still have soap residue or something on me), the coldness of getting out) and lack of motivation (I'm another who can go a long time using only deodorant and not get stinky, although my hair starts looking greasy after a few days). Showering is just a hassle to me.
_________________
Yet in my new wildness and freedom I almost welcome the bitterness of alienage. For although nepenthe has calmed me, I know always that I am an outsider; a stranger in this century and among those who are still men.
-H. P. Lovecraft, "The Outsider"