If you start thinking about it, you will note that females are absent a lot. I was just looking at some publicity for the new Star Trek movie. I saw pictures of at least five males and of only female.

There used to be a movie about an Englishman taken captive by some vaguely-Plains tribe in the 19th century. One day I pointed out to a male friend that the tribe had strange demographics.

"What do you mean?"

"It has only two females in it, one young and beautiful and one old and witchy. (This is the usual combination.) Everybody else is male.
The tribe has are no teenage girls, no young mothers, no baby girls."

"You know, I never noticed that!"

(No wonder that, after the Englishman had been tied to a stake for 3 days and hadn't started growing a beard yet, they decided to rethink this.)

Authors probably don't actually forbid the existence of female dwarves. They don't put them in their books because, like my male friend, they just don't think about them.