I tend to agree with Roger Haller. Never in my 47 horse-years have I seen so many people involved in jumping in general and eventing in particular. I'm not sure what's priming the pump. It could just be that eventing is simply the next in the long list of extreme challenges we seem to need these days to keep us feeling good.
Statistically, the more competitors participating in a sport, the greater the number of accidents will be--not the percentage, but the actual number. The percentage might actually be dropping. I haven't seen any studies to support or refute that.
I think there might be some valid concern over the fact that any barn owner or instructor with an empty field can fill it with jumps and call it a "cross-country course", which I think gives some riders the impression that, if they can make it around at home and do a passable dressage test, they can sign up for the next mini-event without any further instruction. Hopefully the recent increase in the number of eventing clinics held by successful riders will over-balance that trend.
I don't know whether or not it's related, but I've also noticed over the past few years that the quality of riding and of the horses being ridden at local shows has deteriorated while the number of competitors has increased. I'm wondering whether competition is being used as a lure to get more youngsters interested in riding (and keep them interested) to bolster the horse business in a time of economic stress. Not that a shot in the arm isn't necessary and good, but perhaps the competitive drive is pushing the wrong buttons and giving quantity an edge over quality.