In a way it's because the folk tradition was in and of itself masculine. You'd not get too many women in the circles these songs were born in, in the fields and down the pub, and that's the simple demography of the tradition. But that doesn't mean women can't or shouldn't sing them, it means they need to be adapted with intelligence. It's the reason there are so many couple duets around now, because the same tale almost always has two sides, and both need to be shown.
Sure, there are some womens songs, and the idiom's not for the wilting violet or the last remnant of The National Songbook and its heirs. The simple truth is, though, that a woman tackling Roll The Old Chariot Along is not going to be too credible. Unless, that is, she's straight out of Gilray or Hogarth's cartoons of 18th century battleaxes!