I don't think they stop reading in that genre at all, necessarily - they just (well, I just, and I'm guessing I'm not the only one here) drop back from the fandom. Thus: "We know most sci-fi fans are male, because most of the readers of our magazine are male!"
The market tends to work
When all other factors are equal, and when there's no deep-seated pre-existing tendency to cling to a particular belief in the face of the evidence. Alas, this seems to be somewhat of a problem when it comes to such matters - specifically, film and TV. When 50% of your paying viewers are female, and most of your material is still failing the Bechdel test, it's fair to say that market forces might not be the only thing swaying your decision.
no subject
The market tends to work
When all other factors are equal, and when there's no deep-seated pre-existing tendency to cling to a particular belief in the face of the evidence. Alas, this seems to be somewhat of a problem when it comes to such matters - specifically, film and TV. When 50% of your paying viewers are female, and most of your material is still failing the Bechdel test, it's fair to say that market forces might not be the only thing swaying your decision.