Here is the salient point on the Wikipedia page that explains why horses don’t produce 1 HP:
Watt judged that the horse could pull with a force of 180 pounds-force (800 N)
Basically, Watts made up HP to sell his steam engine to mines and likely made up a number to make the new technology seem better.
Some things never change.
Maybe it’s time to go to the court house and change their name to Lua?