There is another factor similar to speed, which is probably less feared but also works the same way. It is distance. The further you go before resting up, the more danger of something going wrong. Of course, anybody can have a crash at any time, even pulling out of your own driveway, but I am convinced that putting on high mileage in one day can be an additional risk.
Here is a story that illustrates the situation. A person sets out to do an Iron Butt "Butt Burner 1000" which is a documented 1000 mile ride, which can be done on your own, in one day. All you need to do is send documented proof to the Iron Butt Association, and you get a certificate saying that you accomplished this mission. A 1000 mile ride is not easy to do, and so according to my theory, you should be extra careful. Especially of the last 500 miles. In this case, the person crashed at mile 997.
As the rider states, no accident can be considered all on its own. It is usually a series of decisions or failures. He then concludes
"The cavalier attitude I had to the whole trip was the root of the accident. I'd done it multiple times, so why not just wing it?"Contributing factors, as I count them:
1. Rain prevented stopping to check route and mileage
2. Not knowing that the trip odometer would reset to zero at 621 km.
3. New bike, unfamiliar road (maybe that should count as two factors?)
4. No tank bag to display route map
5. Lightning storm knocked out power
6. RR crossing sign was down (maybe due to a previous accident)
7. RR crossing surrounded by 10 ft. of metal plate
8. RR crossing on a curve
10. Going around this curve with the surface invisible under a pool of water
11. Going around this curve in the dark.
So as I understand it, he was going to follow a known route to rack up 1000 miles, got confused by the odometer into thinking he was 21 miles short of 1000 miles, then without stopping to recalculate, took a detour to add more miles, then late in the 1000 mile long day, in the dark, on a little used unfamiliar road, after heavy rains, hit an unmarked curve that could not be taken at 40 mph because of the metal plate under the water.
I agree with the riders' assessment. Just because you have done 1000 miles in one day several times before, does not mean that you can do it again without the same amount of caution. Just like doing 250 km/hr several times before safely does not mean that the next time you can assume it will turn out OK, because each situation is different.
The one advantage I can see to riding farther instead of faster, is that the crashes tend to not be as harmful at slow speeds.
I have never participated in this kind of event, even though I sometimes have gone long distances in one day. I belong to the school of "riding to get somewhere" rather than the school of "riding to roll up the odometer", although, in some cases, the difference is so very slight.