The equestrian events reflect the interests of the wealthy Europeans and Americans who established the modern Olympics. In the early days a large number of competitors were military gentlemen, and a lot of those were cavalry types.

To expand on what Mojo said, in the 1948 Olympics one of the Swedish riders was disqualified because he was a sergeant not an officer, which resulted in the Swedish team losing the dressage gold medal they'd won. The rules were then relaxed and the Swedes went on to win the gold in 1952. The '52 Games were also quite famous for another military chap in the equestrian, Colonel Harry Llewellyn (who saw action on D Day and served on Field Marshall Montgomery's) staff)on Foxhunter was part of the gold medal winning GB show jumping team.

Because we must know which countries' horses can jump the highest!

Because it requires a lot more skill than people think - its not all just 'done by the horse'.

no idea but i wish it wasn't