SUPERNATURAL

It's just like those horses to take a story about the time they were too lazy to do their jobs properly and craft it into a legend. Have a look at The Legend of Macha:

This legend consists of a woman of unknown origin, most likely divine, who marries a widower, Crunniuc. She is a skilled runner, and her husband brags to the king, Conchobor, that she can outrun his horses.

Irritated by his boasting, the king forces Macha to race his horses, even though she is very pregnant, close to giving birth. She pleads for a postponement of the bet, but the king will not concede. She races and ends up outrunning the king's horses.

These horses were responsible for pulling the king's chariot. There's a job that could have been done by any number of suitable quadrupeds — bears, sheep, even some especially determined hedgehogs — and instead it goes to horses, because of patronage and racial bias. I reckon they got the job because their fathers were horses.

And do those horses actually use this opportunity to earn an honest living? No. They bludge about while some banged-up sheila carrying twins shames them in a humiliating public defeat.

After a spectacle like that, only horses would have the gall to mosey back to the king's stables and live out the rest of their lives gorging themselves at the government's trough. It wasn't their fault, see? It was magic what did them in.