I am confusing. I guess the author want to express a contrast by using ...not...but rather structure. To negate the forepart proposition, should not we have to insert a "not" to make the part negative?
Original:
She attracted attention not so much because of the qualities of her features but rather because of the naturalness and grace with which her expression moved.
With 'not' added:
She attracted attention not so much not because of the qualities of her features but rather because of the naturalness and grace with which her expression moved.
Source: it is a sentence quoted from much acclaimed Murakami Haruki's novel <1Q84>.
Here is the whole paragraph:
A detailed examination of her face from the front would reveal that the size and shape of her ears were significantly different, the left one much bigger and malformed. No one ever noticed this, however, because her hair nearly always covered her ears. Her lips formed a tight straight line, suggesting that she was not easily approachable. Also contributing to this impression were her small, narrow nose, somewhat protruding cheekbones, broad forehead, and long, straight eyebrows. All of these were arranged to sit in a pleasing oval shape, however, and while tastes differ, few would object to calling her a beautiful woman. The one problem with her face was its extreme paucity of expression. Her firmly closed lips only formed a smile when absolutely necessary. Her eyes had the cool, vigilant stare of a superior deck officer. Thanks to these features, no one ever had a vivid impression of her face. She attracted attention not so much because of the qualities of her features but rather because of the naturalness and grace with which her expression moved. In that sense, Aomame resembled an insect skilled at biological mimicry. What she most wanted was to blend in with her background by changing color and shape, to remain inconspicuous and not easily remembered. This was how she had protected herself since childhood.
