He is doing this because he is at the start of his education. He is still (more so depending on breed) a baby and has a lot to learn. He needs to learn how to start coming down into an outline, by using his hind quarters to push instead of his forelegs to pull him along. This has to be developed gradually by correct riding, and correct feeding to develop topline, as opposed to the overuse of training aids. It might be that your horse is a gelderlander or similiar breeding. They hold their heads naturally higher, as do most carriage type horses as they are bred to do this to look good whilst driving. Invest time and money in a good instructor. Ask him/her to leave you with homework to practice with your horse. Never pull your horse into an outline, or resort to heavy or strong bits without a reason. If you do plenty of transitions, raise your inside hand slightly on a circle or every time you change direction, half halt with your outside rein and little kick with inside leg this should help. Good luck.