Because you need effort + the ability to create value, not one or the other. Some people have one but not the other and seek out help to bridge the gap.
Yes, also effort is something a person can influence directly, while ability cannot or only indirectly (education ...) so it makes sense to focus on things people can influence, but but achievement is the ultimate target.
I don't believe in the least that the only thing a person can influence directly is brute effort, and that's the argument you'd need to make in order to build a case for "effortocracy" over rewarding good outcomes. A whole lot of effort out there in the real world is wasted due to entirely preventable errors and mistakes.