Why do the men knock over so many more hurdles?

Because it's allowed unless it was judged to be intentional or if you use your hand. The lower you get over them, the faster. So ideally, you just brush them. But obviously, they brush them hard enough to knock them over. They need to be careful though because hitting them too hard will slow them down. It's a fine line. I dated a hurdler in high school and she was encouraged to brush just hard enough to tip them, if not tip them over. It's usually the trail leg that you want to hit, not the lead as much. Bad things happen if the lead hits too hard.