Why don't we eat horses?

Like most food aversions, there's no definite explanation:

Horse-eating, or hippophagy, became popular in Europe in the 19th century, when famines caused several governments to license horse butcheries. Today, horse meat is most widely available in France, Belgium, and Sweden, where it outsells mutton and lamb combined. While Americans have occasionally consumed their equine friends during times of scarcity, the practice just didn’t catch on. It may be that so many Americans forged intimate relationships with horses during our founding and expansion that eating the creature seemed morally wrong by the time of the nation’s major food shortages of the 20th century.