While it may be true that on average managers salary is higher than a programmers one, what may be of a personal interest is that some programmer are paid better than some managers. If you want to get a higher salary, you can be a great manager, if you want, but another option can be to become an excellent programmer.

If you really want to understand why managers get more than programmers on average, you should try to understand how economics works, as economics is the science describing prices, money and things like that.

As other replies have already told you, salary (like almost anything in real life economy) is not "fair" in the sense more effort gives you more money, it is a result of free market. If you ask why managers get higher salary then programmers, you should also ask why actors or football players are paid better than scientists or miners.