Aside from the dedication of waking up to practice a sport every morning, think of how much time and discipline is it takes to balance being an amazing athlete with being a great student. They likely have all the mental fortitude and academic talent they need to succeed in college, no question, regardless of if they had a bad test day, or their pencil broke, or they had to use the bathroom and ran out of time, etc.
Someone with As and Bs, maybe a C, who did nothing else of note and managed to get a perfect test score one time doesn’t seem near as surefire a bet. If anything it shows you didn’t apply yourself.