There is, in fact, one primary reason that white guys (and no doubt Asian and black guys too)are attracted to Asian girls.
It's the packaging. The package, and the stereotypes conveyed by the package are what hold the appeal.
They're generally slim, and that means slim all over. You seldom see an Asian girl who's top-heavy, or bottom heavy, or particularly curved in any way.
The shape and angle of their eyes produces an illusion of flirtatiousness and subservience - they are permanently, whether they choose to or not, looking from beneath lashes
The shape of their face tends to to be rounded, with taut skin, and their features tend to be small and delicate within that rounded frame - to the extent of being doll-like, when cosmetics are used to emphasise.
They are petite. You are not going to find an Asian girl who towers over anyone.
They tend to have high, even fluting, voices.
What this adds up to is an overall impression of being childlike, not in a way that calls to a pedophile response, particularly; because they are usually clearly adult, but in a way that stimulates the natural/socialised response of a "strong" male to protect what is apparently fragile. An Asian girl may be hard as nails - just like her caucasian counterpart - but her combination of size, smooth skin, slimness, upward glance and childlike voice will make her present as intensely "feminine" in the old damsel in distress fashion, right before she beats the shit out of you on the judo mat. This is especially true, of course, in girls raised within Asian cultures, which emphasise specifically feminine behaviours for women, but is also evident in Asian girls raised in Western traditions.
This is not meant as any kind of derogatory judgment of men, or Asian girls, but an analysis of the artifice of nature. The physical peculiarities of the young Asian female are such that she tends to present to men partly as a little girl - and nothing is more guaranteed to arouse a tender, protective response than a girl-child -- and partly as a flirt, sexually available and challenging but ultimately non-threatening. It's hardly surprising, then, that men are attracted.
You'll note that throughout, I've used the word "girl", rather than "woman". This is because with age, the particular attraction of Asian over other races of women fades fast. When the illusion of childishness disappears, so does the intense aura of femininity, slimness becomes gauntness and tendency to lack curves can often lead to an almost genderless appearance in middle-age and beyond, where other races of women retain a greater level of feminine allure (Yoko Ono, as compared to Susan Sarandon, for example).
Oolong reminds me that I should specify that I'm speaking of East Asian women in this write up. He's right, I should.