but if you jump higher and higher wouldnt they realize once they knock down some poles and it hurts that they need to lift there legs higher?
Some horses, yes, do make attempts to jump better and eventually figure out that picking up their knees and tucking their lower limbs makes for an easier jump. Some horses are lazy over the little stuff but really make an effort over bigger stuff. Some horses are just lazy and don't want to work that hard or just don't care about hitting poles. Some horses physically can't snap their knees up as well. The chestnut in the picture just looks a little lazy. His knees really aren't too bad, but the rest of his legs are drapey. The dark horse? Looks dangerous!