I think you have to remember these were youth showing. Have you ever been in that arena? It overwhelms kids, people and horses sometimes. It is also a good 30 degrees cooler than outside. That sometimes revs up a horse! I know our little Dillon (5 years old) went into hunter this morning and since he is so small, he didn't get his arm up high enough, his shank pulled down the first jump, he just stood there and wondered what to do. He was so flustered he didn't realize he could go on and jump! And yes, he has gone in jumping several times. It all comes down to he is just a kid! Tonight in jumping he knocked down the first two jumps, (him, not the horse), but at least he did his pattern correctly, and finished the course. He got over some of his nerves and managed to get his arm a little higher over the last four jumps. He didn't place, but there are a kajillion of his friends and family that are very proud of him.
Yes, I'm sure there are a few that just went in because they are there, but with 19 horses with a clean round in the under 12-under, I am sure most of them have been in the classes before.