First of all, I would like to say that every successful sportmen don't make too much money. No doubt, there are many great athletes who wait to be discovered.is it only success or chance? Answer of this question has so deep meaning.
In my opinion, all human have a need to be respected and it is difficult to overcome this instinct. Therefore, the fame always becomes more valuable for people and this is because, everyone wants to be famous. For example, a movie star is not a star unless crowds recognize him or her. Fact is that sport professionals are living like movie stars.
Neverthless, sportmen have more diffirent responsibilities than a doctor or an engineer. They have to obey hard diets through their career. They always have to try to find where they can stay lonely, far from the spotlights. They always have to do practise to succeed in olimpics or in competitions. Also pressure of team and audiences on them is not insignificant. So, many people think that all of these factors may justify huge earnings. Maybe it is fair, maybe not.
Actually,these earnings reflect what society value or respect more. Unfortunately, money has become a measure of fame and success. For instance a football star get more money than a basketball player. A basketball player get more than a tennis player. A tennis player get more than a chess champion.
In conclusion, many people set their goals according to society's expectations and values and some of them earn huge salaries. This is important why many young people want to be a football star. Fair is a controdictory fact which shapes in structure of society.