Hills on Roadie verse MB

I’ve been watching some of last years Leadville 100. I don’t know anything about MBing and I only watched very limited footage so this may not be accurate.

Why do MBers tend to stay in the saddle longer than roadies on uphills? It seemed like all the climing footage had them seated.

Traction. On a MB often times if you stand up, you shift your weight forward and the driven wheel (rear) will start to slip because no enough weight is being applied to it. On the road this is rarely an issue (though I’ve been on some super steep hills that when wet you have to do seated)

Makes sense. Thank you sir!