It's not that hard to understand at all. But is it a matter of divergence of taste, or a matter of going against the majority? I'm sure there are those who truly do not find her attractive, but I would imagine that a fair chunk of the others are just trying to seem coolly indifferent. "Who? Britney Spears? I'm not impressed." By doing this, you pretty much imply that your sexual tastes are much more sophisticated and refined than the general population, and that you have much better women as your sexual standard. Not saying that all do this, but there has to be quite a few of them.