Why are so many common Asian names English genitalia euphemisms?

Long before the names Poon or Dong were common in America (though Wang, or Wong --most Americans don't distinguish them -- has been known here as a Chinese name for over a century), the euphemisms

• poon < poontang < putain < Fr pute, 'prostitute'

(for female genitalia), and

• wang /wæŋ/ < wangdoogle, nonce phrase for 'thing'
• dong < dangle, 'to hang down as a pendulum'

(for male genitalia),
and many more as well, for both, were making the rounds of the English-speaking world.

English, since its speakers have many strange beliefs and taboos about the power of word magic, has to use an enormous number of euphemisms in order to avoid taboo words. One is reminded of the Nacirema.

These euphemisms change constantly, of course, like any other fashion, and, if allowed to fester, will use up every available syllable.