There simply weren't that many of them, because the opportunities were few and far between.
Being a prematurely aged bastard, I listen to Radio 3, and they feature old-time black and female composers all the time - disproportionately often, in fact. They have whole programmes about them. Of...
I take it you've heard this, or some variant of it:
Conservatives - "It's fine that ten people own half the world's wealth."
Socialists - "No it isn't."
Liberals - "FIVE OF THOSE PEOPLE SHOULD BE WOMEN!"