That is a heavy question, and it applies not only to jazz, but to music in general. Why are there so few women who are instrumentalists? Do they feel pressured to become singers? Do we, as a society, accept women who play drums, play guitar, play saxophone, the same as men?
Since I have a daughter now, and she is already very musical, I've wondered the same things. It is my goal to make sure she understands that she can play whatever instrument she wants, in whatever style she wants, and she does not have to take a back seat to any man.