Riders completion rate
I would suggest that the biggest influence would be the diffence in weight. In the old days a cagiva or teneree or BMW would have been about 300 kg once loaded with 40 litre of fuel. The new 450 's would be about 170 kg loaded . Sand riding with the big old girls would have been something that very few riders could do well. The 450's with less weight would mean that the average rider has a chance of making it through the more technical sections.