It does seem rather strange that horse racing is also known as the "sport of Kings", but as in everything, there is a fairly good explanation, of which, long before cars and other modern means of transportation were invented, the dividing line between those that had money and those that were peasants with little rights or money, was the ownership of a horse, and in particular, a riding horse, that enabled those that owned such, to travel from one place to another, in order to conduct business, or to visit other estates, or for the visitation of churches, and other such things, in which, the riding of a horse was not only the easiest and most efficient way to get from one place to another, but often necessitated a large retinue of additional horses and personnel to assure that such a journey was successful and safe.
So too, a man on a horse, is an entirely different creature than a man without a horse, for a horse allows both mobility as well as leveraged status by virtue of height as well as by the control that a man has over an animal that can easily weight over 1,000 pounds and be five feet or higher while just standing on its own four legs, not to mention the sheer strength and power of a horse that is able to carry a man at a good gallop for several miles. In all of this, those that mastered their own horse, demonstrated to all others without a horse, their strength and status.
Not too surprisingly, sporting activities, for entertainment, fun, and wagering, has been a part of civilizations for centuries, so that, those that owned horses, created a dividing line, between sports that utilized horses, such as in polo, or horse racing, amongst other things, as compared to other sports, that because the participants could not afford a horse, had to be played on foot, such as football or soccer, and basically all of the most popular sports of today.
This means, that those sports that necessitate a horse, are in many ways, a reflection of class status, of which, for instance, in horse racing, in order to own a horse, train that horse, harbor that horse, and be competitive utilizing that horse, necessitates the expenditure of a lot of money, which means that only those with such money participate, with the actual rider of the horse, basically representing a well compensated employee of the owner, but is never considered part of the same social status or milieu.
Indeed, in sports, social status is shown, of which, those sports that necessitate a horse will only attract those that have money, and usually a historical interest in such, as well as those sports that necessitate a fast car, will only attract those that can afford the upkeep and the expense of racing cars, of which, the more expensive the sport is, the more exclusive that sport is to the true participants of it. So that, your basic sports that just require a physical body, and a relatively small expenditure of money for shoes, uniforms, and other assorted items are for one class of people, and all those other sports that necessitate a rather large capital outlay are for those that may not be kings in name, but act and are treated in many ways, as if they are royalty.