It may have something to do with what we learned as children. Even though I grew up at various places in the west, back when I was young, far fewer parents got their girls involved in camping than happens now. If you don't grow up camping, it can be a tougher adjustment than for someone who learned at an early age.
Back 30 years ago, I met a woman when I was on a backpacking trip. We'd come in from different directions, but no matter how you hiked, it was still a 30 mile trip to where we were. We ended up dating for a few months. I do see women backpacking today, but rarely alone and rarely so far in.