Considering a typical horse produces about 1-14 HP*, it’s possible to run the horse for several hours at a time, change a battery, and run an efficient router off of it each day.
*sauce: https://www.sciencefocus.com/science/how-much-horsepower-does-a-horse-have
It’s not the only country. I’ve lived in another country that was just like that. I bet other countries have the same rule to avoid some tax loophole. Or just because they can.