He was the only trail leader. Since it was his last run everyone wanted to stick with him and he needed some others to take the other group if they wanted to do hard.
We also had a guy tag along with just a small suspension upgrade who was supposed to meet his friends at the camp ground to go hit the trails and they all bailed on him. So it worked out well as he was challenged, and everyone else just wanted to send off their leader in style.
I think that's why they did some other runs later in the evening and morning, so folks that wanted some more difficult runs could get them in.
That's all just an assumption as it wasn't really covered at the drivers meeting.
Regarding his wheel ... who knows? Maybe the lugs weren't tightened all the way and spun off, then the others sheered under stress of the trail rocks and bumps.