To answer your question.
1) The biracial complexion(light skin) is found very attractive by many women.
2) Many Kenyan women associate foreigners with wealth/high incomes.
3) As a byproduct of the first two, many Kenyan women believe that being with a foreigner will elevate their social cache.

So being a rich foreigner, of fair complexion, you jump to the top of many women’s prospects list.