Why do colleges accept students who excel in sports while having bad academic merits?

At a local university, one of the alumnus told his story that he got accepted because he was the captain of the track team but he had bad grades. College is a place to learn, why would they admit someone with poor educational history just for him/her to play on their team and end up not being able to graduate(maybe)? I remember reading a book by Delbanco, he said something of the likes of "I will not admit a student to kick a leather ball" something the likes of that.

Edit: thanks alot for all of your good answers! As a college student, your answers helped me understand more. This question blew up, inbox is all red. 
Athletics affect grades in a negative way because student athletes take easier classes and get lower grades than non-athletes [3]. This is not only true for schools from power conferences in big-money sports, it has been observed in Division III liberal arts colleges and Ivy League schools, neither of which even offer athletic scholarships [3].
One reason students with poor academic merits can still get into college is because they excel in sports. Sometimes, student-athletes did not meet the academic standards of their university but were admitted anyway because of their sport. [1] School sports departments and coaches can also place more of an emphasis on athletics than academics. For example, some coaches believe that college athletes shouldn't worry about school; they should just focus on their sport. [2] In addition, college admissions boards know that being part of a team sport requires a significant amount of time and commitment. Without further investigation, it's hard to say whether a chess club member had a weekly commitment of 20 minutes or 20 hours. College admissions boards are aware of the level of commitment that is required for playing a varsity sport, such as soccer. [6] Therefore, student-athletes can sometimes get into college because of their athletic involvement, despite having poor academic records.