Here's why:
* Historical reasons: Historically, racetracks in the US and many other countries were built with the majority of the turns going to the left. This led to horses being trained to run with the rail on their left, and this tradition continues today.
* Natural instinct: Horses are generally right-handed, meaning they tend to favor their right hind leg. This makes it easier for them to turn to the left, as their right hind leg is stronger and helps them maintain balance.
* Safety and efficiency: Running on the left side of the track allows horses to navigate turns more smoothly and avoid crowding other horses.
While there are a few tracks around the world that have a right-handed configuration, the vast majority of racing tracks worldwide are left-handed.