Pay isn't just relevant to effort spent either, it's also an inventive to fulfil responsibilities

For example, let's take the average retail store
You have shop workers earning the least. Their responsibility is listening to what the manager says, and doing it. Keeping everything stocked and tidy
Then you have supervisors, they have an increased level of pay due to increased responsibility
They are there to ensure the workers are carrying out their orders, and the shop is running efficiently
Then you have management, who take the big decisions in what direction the store is going to go, they are responsible for a lot more money than the workers are - they use the literal budget of the store

So they get paid more, to ensure they wish to do the best job they can, to continue getting paid that much
If they got paid fuck all, they'd move onto somewhere else, and try harder at another place whom would pay more