I am going to make the effort to provide an answer anyway. But make no mistake, this really shouldn't be something to question.
NOTE: Family, as always I apologize for the lengthiness but, it was necessary I felt to school the rule here if you feel me.
The reason, honestly, is simple: Because Professional Sports are hazardous jobs and athletes are a form of marketing the product (The Team and/or The League)
I'll stick to the American sports NBA, NFL and MLB .
Scenario 1 - NBA: You work for $20/hr playing in an NBA game as a player and then you blow your knee out 2 mins into 3rd qtr. Your illustrious career of not even playing in a whole game ending on a freak play. you earn idk maybe $25 because one half of basketball is maybe 75mins of work, since most basketball games average 2.5.hrs long.
Question: Does $25 for one half of work and a lost career sound like fair compensation to you? After all the working out and keeping your body conditioned all year long. Having to give up certain activities so that you DON'T end up injuring yourself outside of basketball activities. ONLY for this to happen and all you have to show for all that work you put in is $25?
Scenario 2 - NBA: Let's say you complete one NBA game and as I stated before, most games run for about 2.5hrs. You run up and down a court getting physical with opposing players throughout a tough contest. By the end of the game you made $50. That's less than one courtside seat.
Question: You think after all the energy expended for those 2.5hours then needing to put in all the work that is required to get your body ready and reconditioned for the next game is only worth $50 of compensation? Less than one courtside seat?
Scenario 1 - MLB: Let's say you make $40/hr in a game. Every inning is about 20mins to get through for an average 3-hr game. You step up to the plate it's the second inning and you get beaned in the head with a 99 mile an hour fastball. You get carted off the field, fall into a coma and die. You made it through 1 inning which is 20mins
Question: Do you think after that your family that you leave behind is fairly compensated with your $13.34 worth of game check?
Scenario 2 - MLB: You play in a full 9-inning game running an average of 3hrs. You hit a homer, stole a base, threw a runner out stealing, made a daredevil catch in foul territory. But you only made $120. And what's more, you get to get up and put in that same amount of energy and effort the very next day because baseball is played daily during the season save for the occasional off day.
Question: You think on a 11 game homestand, playing for 3hrs every day putting it all on the line in each and every game you should only make $1,320?
Scenario 1 - NFL: You play in an entire NFL game. Avg runtime is about 3hrs. You only play once a week so you make $15/hr.
After the game, you're in the locker room and you pull something in your lower back and now you're out of the line up for the next game. So after 3 hours of tackling being tackled, throwing, running, catching, kicking or whatever you did in the game, you made $45 and you know for at least one game, you're not going to playing.
Question: That sounds like fair compensation after all of that?
Scenario 2 - NFL: You never even got to play in the game because it was discovered that you have severe CTE from your college playing days. So now you've been cut by the team and you have no means of income because all your hopes were riding on making it in the NFL.
Question: All that for nothing sounds pretty fair right?
Now looking at it from the athletes are live action marketing reps. The guys that become superstars and faces of franchises and faces of leagues are putting asses in seats in every stadium and arena at every game, are selling out merchandise and are bringing in sponsors to teams that very well may never have even been on the radar before. When YOU'RE the reason people pay to watch, you got damn right they better pay in millions ESPECIALLY when that player is the reason the league and the team is MAKING millions.