Horses tend not to run for office. Because they're horses.

Everyone knows someone who worked for years on a project only for it to go nowhere. Pour years into a business that failed. Spend years getting a degree that was useless. Effort might be a part of many people's success stories, but it's not the thing that literally gets rewarded. And conversely, many people get rewarded for things that require relatively little effort.

I suppose I should have said that the correlation between effort and reward has never been 1.0 and has often been a lot lower than we like to believe.

The same aversion to leadership positions can be seen in most engineers. The difference is: the horse doesn't expect a promotion to happen by itself.