Why do sports coaches make so much money?

First, we should note that not all sports coaches make a lot of money. The vast majority of people that coach even at the NCAA Division I level do not make the astronomical salaries we associate with the profession. But, to keep the answer in American college sports, the average salary among major college football coaches in 2012 was almost $1.7 million. This is more than three times the average salary of the college presidents that employ them and many times higher than the salaries of teaching faculty. Division I college basketball coaches, on the other hand, also earn massive salaries, with the highest paid coaches earning in excess of five million dollars a year. In professional athletics, coaches are generally paid even higher salaries. The highest paid NFL coaches, for example, make more than eight million dollars a year. Note that these figures do not even include additional money from product endorsements, public appearances, and other sources which in many cases actually exceed salary figures. Whether in the pros or college, the reason sports coaches make so much money is largely based on the massive stakes in winning and losing. Both college basketball and football, as well as all major professional sports, are multi-billion dollar industries, and the most successful teams bring in millions in merchandising, television rights, and other funds. So the stakes in hiring a successful coach are very high. At the college level, there is also considerable pressure from wealthy donors and fans to choose high-profile coaches. So in short, there is a very high demand for good, highly-qualified, well-known coaches, and these are in short supply. Colleges and pro teams have to compete for them, and offer exorbitant salaries to attract them. 
https://careertrend.com/much-average-division-football-coach-earn-28837.html

https://www.theatlantic.com/education/archive/2016/03/the-madness-of-college-basketball-coaches-salaries/475146/