"6500 registered"
That's primarily why I would never enter one of these.
In general, committing a lot of time and resources to any single event like this - that that can go wrong very quickly for many reasons - has always seemed like a bad idea to me. You are in France, so not as big a stretch as for many of us. I've had friends who've flown to Europe for large single day event who've had such bad experiences that they felt they wasted a year of their lives in preparation.