@FlowersInDenmark women do relatively well in ultras compared to shorter races (though women don't beat men in marathons, do they?) If you're involved in volunteering at ultras you should know this. Suggested reasons include
Fat metabolism: Women tend to burn fat more efficiently, giving them a steady energy source over ultra distances.
Pain tolerance and pacing: Studies show women pace more consistently and may manage pain and discomfort more effectively.
Mental endurance: Ultrarunning is as much mental as physical, and women are shown to be more resilient in the face of fatigue, cold, sleep deprivation, and discomfort.
(from https://www.ratrace.com/blog/how-women-are-taking-over-the-ultramarathon-world/)
So how come you don't also know that orienteering races are generally not as long as ultramarathons, and they are not just about mapreading?
And as others have said, even if there were no advantage/disadvantage for men vs women, women are allowed to have our own categories without including men.