Word on the radio seemed to be that a lot of the cars that would have raced had only just returned from the Le Mans Classic, and weren't ready to be run again quite so soon. The older the machinery is, the more work it takes to keep them in running, let alone racing order, and I guess most of them are privately owned and can't have a full factory team working around the clock to get the cars ready for the next event.
Shame though, once the field spread out I guess they all had a pretty lonely time of it (except the two Lolas!). Still, I'm glad those that came did run - I'd never seen a 917 in the "flesh" before