The top photo is of an event rider over a drop fence; which is why you see the rider taking a somewhat defensive, safety position. Notice that the horse is happy, ears forward, that the rider has slipped the reins and is not interfering with the horse.
When I was new to eventing, and believed every riding situation could be handled from a classic forward seat, I attended a terrific clinc with the great Jimmy Wofford. During the lecture portion, I asked a politer version of "Why are eventer's positions so ugly?" and I got two answers from Mr. Wofford. First, "No Italian ever won the Grand National" (Italians - pioneers of the forward seat; Grand National = classic British steeplechase with horrific drop fences) and second, not taking the defensive position violated the first rule of equitation.
Dead silence among the clinic participants.
Mr. Wofford "You all know the first rule of equitation, right?"
Embarassed silence as a group of experienced riders scavenge their memory for the first rule of equitation. Heels down? Head up? Don't interfere with your horse?
Mr. Wofford "Don't fall off. Nobody can judge your equitation if you're sitting on the ground."
Staying in two point while negotiating a drop greatly increases the chance the the horse will misstep and send you over his ears.
The second photo is of a lovely, classic, correct forward seat rider.
The third rider got left, plain and simple.