If you ask why women do not have beard and mustache, it is like asking why males do not have female private parts and females have no private parts like males; cannot answer such questions for there is no answer.
At birth you do not have mustache, beard, axilla hairs and pubic hairs; so they are unwanted for the natural beautiful growth of children male or female. Hence, it is not necessary and it is of no use, even after you had reached the adulthood.
Nowadays females want to be equal to males, god willing, they may develop beards and mustache in the near future.